JP3984187B2 - Manufacturing method of optical attenuator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the production how optical attenuator attenuating the transmitted light is absorbed in the OH group or OD group increased in the optical fiber.
[0002]
[Prior art]
Quartz-based materials are used in many fields such as optical communication waveguides and optical lenses because of their excellent light transmission. In particular, optical fiber materials used in optical communication lines are made of silica, so functional optical components such as optical wavelength-selective filters, branching / combining devices, demultiplexing / multiplexing units, and attenuators are created in the line. In consideration of the refractive index, the core diameter, the melting point at the time of fusion splicing, and the like as the connectivity with the optical fiber, there is an advantage in manufacturing these functional optical components from the quartz-based material.
[0003]
Light that reduces the light intensity using an appropriate method when the light intensity of the signal light of the optical communication line, the light source of the optical measuring instrument, or the optical sensing system is excessive compared to the purpose. An attenuator is required.
[0004]
As an intended use of the optical attenuator, when signal light is incident on a photodiode (PD: Photo Diode) or an avalanche diode (APD) which is a light receiving element while the transmitted signal light intensity is high, a unit area is obtained. Since the light intensity per unit is high, there is a risk that these light receiving elements are destroyed, so that it is necessary to reduce the signal light intensity.
[0005]
Another purpose of the optical attenuator is to emit signal light of several tens of wavelengths from an optical transmitter and a repeater in high-density wavelength division multiplexing (DWDM) (hereinafter abbreviated as DWDM). This is because sometimes it is necessary to equalize (equalize) the signal light intensity for each wavelength.
[0006]
In general, optical attenuators can be broadly classified into (1) a fixed attenuator having a fixed attenuation value and (2) a variable attenuator capable of changing the attenuation value. Further, among the fixed attenuators, the main functional optical components are (1-A) a fiber type optical attenuator made of an optical fiber and (1-B) a micro-optics type employing micro optics such as a lens and a prism. It can be classified into optical attenuators.
[0007]
Here, mainly (1-A) fiber type optical attenuator among (1) fixed optical attenuators will be described below.
[0008]
As a method of manufacturing a fiber type optical attenuator, as shown in FIG. 8A, a metal ion (eg, cobalt ion) is added to the core 101 of the optical fiber to absorb the incident signal light 115. The method of making it do is reported in Patent Document 1.
[0009]
Further, as shown in FIG. 8B, there is known a method in which the incident light beam 107 is absorbed by the metal thin film 109 by cutting the optical fiber with a slitter and inserting the metal thin film 109.
[0010]
Furthermore, as shown in FIG. 8 (c), there is a method for scattering incident signal light 117 by heating a part of an optical fiber at a high temperature and enlarging the diameter of the core 113b over a certain length. 2 is reported.
[0011]
Also, as shown in FIG. 8D, a fiber Bragg grating (hereinafter referred to as FBG) 125 is formed on the core 121 of the optical fiber to reflect the signal light 127 having a specific wavelength and transmit the transmitted light 129. A method of attenuating the frequency is reported in Patent Document 3.
[0012]
As an application field of the FBG125 DWDM system shown in FIG. 8D, there is an application example as a gain equalization (or flattening) filter of an optical amplifier as shown in FIG. In a DWDM long-haul trunk optical communication line, in the wavelength range λ1 to λ2 of optical amplifiers (1530 to 1565 nm in the C-Band example), the gain after optical amplification generally depends greatly on the wavelength, Although the difference between the maximum gain and the minimum gain (hereinafter referred to as gain flatness) is several dB, the gain flatness can be suppressed to about 0.5 dB by using the FBG 125 as a gain equalization filter. .
[0013]
However, in the case of a trans-Pacific optical submarine cable as long as 10,000 km, in the wavelength range λ1 to λ2 of the optical amplifier, the gain slope, which was negligibly small in each optical amplifier stage, is the number of repeater stages. When the number of stages reaches approximately 200, the gain slope is accumulated, and the problem that a gain slope of α dB between wavelengths λ1 and λ2 occurs after multi-stage relay as shown in FIG.
[0014]
In order to compensate for this inclination, by using an optical attenuator (see FIG. 11) having a loss inclination equal to the accumulated gain inclination after multi-stage relaying, as shown in FIG. Obtainable. Here, as shown in FIG. 10, the optical amplifier gain after multistage relay is not always high on the short wavelength side and low on the long wavelength side, and vice versa.
[0015]
[Patent Document 1]
JP-A-9-2351329
[0016]
[Patent Document 2]
JP 10-268153 A
[0017]
[Patent Document 3]
JP2002-267848
[0018]
[Problems to be solved by the invention]
By the way, as shown in FIG. 8 (a), in the method of producing a special fiber in which metal ions are added to the core of an optical fiber, the base material (preform) must first be produced in order to spin the special fiber. did not become.
[0019]
Compared to the general transmission optical fiber market that is produced on a large scale, the market scale of special fiber doped with metal ions, which is one of the fiber type optical attenuators, is much smaller. As a result, there is a problem that spinning a special fiber from a small base material becomes very expensive.
[0020]
On the other hand, with respect to the method shown in FIGS. 8B to 8D using the general transmission optical fiber produced on a large scale, the optical fiber itself is inexpensive and easy to obtain. Since precise processing is required to attenuate the light, there is a problem that it becomes expensive as a result.
[0021]
Furthermore, as shown in FIG. 8D, the method based on the reflection of light by FBG formation requires an excimer laser that emits coherent ultraviolet light. This excimer laser has a problem of requiring a large investment as a manufacturing facility.
[0022]
The present invention has been made in view of the above, and as its purpose, an inexpensive general transmission optical fiber that is mass-produced without using any special fiber that is inevitably produced in small quantities and is expensive. It is an object of the present invention to provide a manufacturing method and a manufacturing apparatus that can be easily mass-produced as materials, do not require precision processing, and do not require expensive capital investment.
[0023]
[Means for Solving the Problems]
In order to solve the above problems, the invention described in claim 1 is a diffusion process in which deuterium is pressurized and diffused into the silica-based optical waveguide, and a light source is provided in the silica-based optical waveguide in which deuterium is diffused by the diffusion process. Irradiating incoherent ultraviolet light from the irradiating step to increase the OD group in the silica-based optical waveguide, and after the irradiating step, heating the silica-based optical waveguide to release the remaining deuterium to the outside And a heating step that absorbs the signal light in the increased OD group in the quartz optical waveguide and attenuates the signal light.
[0024]
In order to solve the above-mentioned problems, the gist of the invention described in claim 2 is that the light source comprises an excimer lamp that emits ultraviolet light having a wavelength of 172 nm.
[0025]
In order to solve the above-mentioned problems, the gist of the invention described in claim 3 is that the light source comprises an excimer lamp that emits ultraviolet light having a wavelength of 222 nm.
[0026]
In order to solve the above-mentioned problems, the quartz-based optical waveguide includes at least one of germanium, phosphorus, and boron as an additive material for increasing the absorption of signal light. The gist.
[0027]
In order to solve the above problems, the invention according to claim 5 is characterized by having a light control step of inserting a filter for adjusting the intensity of ultraviolet light between the light source and the silica-based optical waveguide.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0029]
(First embodiment)
FIG. 1 is a diagram for explaining the configuration of a fiber-type optical attenuator 11 manufactured by an optical component manufacturing method according to the present invention.
[0030]
The optical attenuator 11 is obtained by cutting the optical fiber 13 into several meters and removing the coating at the intermediate portion, and transmits the incident optical signal to give a predetermined attenuation characteristic and emits it.
[0031]
Next, the manufacturing method of the optical attenuator 11 will be described with reference to the manufacturing process flow shown in FIGS.
[0032]
In the process P1 shown in FIG. 2, the optical fiber 13 is accommodated in the high-pressure vessel 21 as shown in FIG. The shape of the optical fiber 13 at this time may be a coated optical fiber wound with a reel exceeding kilometer, or a coated optical fiber cut to several meters to several hundred meters.
[0033]
Next, with hydrogen (H 2) or deuterium (D 2) filled and pressurized to 100 atm, the temperature is maintained at 55 ° C. and left for 1 week to pass hydrogen or deuterium on the cladding of the optical fiber 13. Spread through to the core. For this purpose, in the state where hydrogen or deuterium is diffused in the core of the optical fiber, excimer that is incoherent ultraviolet light (UV: Ultra Violet, hereinafter referred to as UV light) in the process P2 shown in FIG. This is because when the lamp light 33 is irradiated, hydrogen (H 2) and oxygen in quartz (SiO 2) or germanium dioxide (GeO 2) combine to increase the concentration of hydroxyl (OH) groups. When deuterium is diffused into the core, the concentration of OD groups in quartz is increased.
[0034]
In the process P2 shown in FIG. 2, as shown in FIG. 4, the excimer lamp 31 that can irradiate a wide area of 500 mm × 80 mm, such as the excimer lamp light 33, is used to pass hydrogen (H 2 Or a large number of optical fibers 13 diffused with deuterium (D2).
[0035]
At this time, the intensity adjusting filter 35 is used when the light intensity of the excimer lamp light 33 is too high. When the light intensity of the excimer lamp light 33 is appropriate, the intensity adjusting filter 35 is not used. By the irradiation of the excimer lamp light 33, absorption of signal light having a peak at 1390 nm occurs in the core 27 portion where the OH group has increased, and an optical attenuator is formed.
[0036]
The wavelength of the excimer lamp light 33 necessary for producing the optical attenuator usually needs to be 280 nm or less, although it depends on the sensitizer to be added. This is because photosensitivity is very small with incoherent UV light of 280 nm or more, and it is difficult to obtain a desired change in light attenuation. On the other hand, excimer lamp light of 150 nm or less absorbs excimer lamp light in pure quartz without adding a sensitizer, and the excimer lamp light does not reach the core center, so the irradiation wavelength must be 150 nm or more. There is.
[0037]
Here, germanium, phosphorus, boron, etc. are mentioned as a sensitizer which raises photosensitivity. Usually, germanium is added to the cores 25 and 27 of the optical fiber in order to increase the refractive index. Therefore, it is not necessary to add an additional sensitizer.
[0038]
The same phenomenon occurs in an excimer laser that emits coherent UV light instead of the excimer lamp 31 that emits incoherent UV light. However, compared to the excimer lamp 31 that is inexpensive, can irradiate a wide area, and is easy to handle, the excimer laser has a drawback that it is very expensive, has a small irradiation area, and is not easy to handle.
[0039]
In addition, the excimer laser is a pulsed laser and is irradiated with a large amount of energy instantaneously, which may damage the optical fiber surface and degrade the optical fiber strength. However, when a lamp is used, the energy density is lower than that of the laser. Since it is about 1/1000, there is an advantage that strength deterioration does not occur.
[0040]
Further, by using a light source such as an excimer lamp that emits light with a narrow spectral line width in the ultraviolet region, it is possible to efficiently increase the absorption of light energy in the waveguide.
[0041]
Next, in step P3 shown in FIG. 2, as shown in FIG. 5, a large number of optical fibers 13 are stored in an oven 41 and left in a state heated at a high temperature for a certain period of time to diffuse into the optical fiber 13. Hydrogen (H 2) 43 or deuterium (D 2) can be released into the oven. Thereafter, the residual concentration of hydrogen (H2) or deuterium (D2) in the optical fiber 13 is sufficiently reduced, so that the characteristics hardly change even when stored for a long time.
[0042]
In the case of the optical fiber 13 in which hydrogen (H2) is diffused in the process P1 described above, the optical attenuator 11 manufactured by such a method has a signal light loss peak at a wavelength of 1390 nm due to the increased OH group. Arise. On the other hand, in the case of the optical fiber in which deuterium (D2) is diffused in the above-described process P1, the peak of signal light loss occurs at a wavelength of 1870 nm due to the increased OD group.
[0043]
Even at a wavelength other than both peak wavelengths of the light absorption peak wavelength 1390 nm due to the OH group and the light absorption peak wavelength 1390 nm due to the OD group, the signal light is attenuated to some extent, if not as much as the peak wavelength. In order to obtain a larger attenuation amount at a desired signal light wavelength, it is only necessary to increase the OH group or OD group in the core. As the method, in the above-described step P2, excimer lamp light is used for a long time. By irradiating 33, a large attenuation can be obtained. As another method, the optical attenuator 11 having a large loss in proportion to the length of the core in which the OH group or the OD group is increased in the length direction of the optical fiber. Is obtained.
[0044]
(Example)
Here, the result of actually manufacturing an optical attenuator using the manufacturing process and the optical component manufacturing apparatus shown in FIG. 2 will be described.
[0045]
The optical waveguide using its general transmission silica-based single mode optical fiber comprising a zero dispersion at that widely used 1300 nm. The core of the single mode optical fiber is doped with about 3.5 Wt% germanium dioxide (GeO2), the diameter of the core 25 is about 10 microns, and the relative refractive index difference between the core 25 and the clad 29 is 0.35%. is there.
[0046]
In step P1, the optical fiber 13 was left in a hydrogen atmosphere at 55 ° C. and 100 atm for 1 week to diffuse hydrogen (H 2) into the core 25. Next, in step P2, excimer lamp light 33, which is incoherent UV light from the excimer lamp 31, was irradiated. Here, the wavelength of the irradiated excimer lamp light 33 is 172 nm. If the optical fiber coating was present, the excimer lamp light 33 did not reach the center of the core 25 sufficiently, so the coating 15 was removed.
[0047]
As described above, the optical fiber 13 diffused by hydrogen into the core 25 and the coated optical fiber 13 is irradiated with the excimer lamp light 33 from the excimer lamp 31 having a power density of 15 mW / cm 2 for 10 minutes, and then transmitted through the optical fiber 13. Changes were measured. FIG. 6 shows the resulting wavelength loss characteristics. As shown in FIG. 6, a light absorption peak due to the OH group was confirmed at a wavelength of 1390 nm.
[0048]
Next, FIG. 7 shows the relationship with the transmission loss at 1390 nm when the irradiation time is changed under the same irradiation conditions. As can be seen from this, as the irradiation time of the excimer lamp light 33 of the excimer lamp 31 becomes longer, the OH groups in the core 27 increase and the light loss increases. Therefore, a desired loss can be obtained by changing the irradiation time.
[0049]
Although not shown, in an optical fiber in which deuterium (D2) is diffused into the core 27, a light absorption peak of an OD group exists at a wavelength of 1870 nm.
[0050]
The main wavelength bands used in the DWDM trunk line optical communication network are currently C-Band (1530 to 1570 nm) and L-Band (1570 to 1610 nm). In the DWDM system using C-Band and L-Band, as shown in FIG. 10, the gain characteristic of the optical amplifier after the multi-stage relay is such that the gain of the short wavelength λ1 [nm] is longer than that of the long wavelength λ2 [nm]. In order to compensate for the gain tilt when the slope is increased by α [dB] higher than the gain, the loss of the short wavelength λ1 [nm] is reduced to the long wavelength λ2 [nm in the same C-band wavelength region. ], An optical attenuator having a loss slope that rises to the left is larger than α [dB].
[0051]
As shown in FIG. 6, the optical attenuator 11 in which the OH group is increased with an optical fiber in which hydrogen (H 2) is diffused has a light absorption peak at 1390 nm, and its base C-Band (1530 to 1570 nm). And L-Band (1570 to 1610 nm) have a loss slope characteristic that rises to the left, which is suitable for this purpose.
[0052]
On the other hand, in contrast to the case shown in FIG. 10, when the gain on the long wavelength side of the optical amplifier after the multi-stage relay is a rising slope that is higher than the gain on the short wavelength side, Requires an optical attenuator having a loss slope characteristic that rises to the right. For this purpose, in an optical attenuator in which deuterium (D2) is diffused into the core to increase the OD group, a light absorption peak exists at 1870 nm, and the C-Band (1530 to 1570 nm) and L-Band at the base thereof. At (1570 to 1610 nm), the loss slope rises to the right, which serves this purpose.
[0053]
Although the measurement result is not illustrated, the same optical attenuation result is obtained when the wavelength of the excimer lamp light 33 which is the incoherent UV light of the excimer lamp 31 is set to 222 nm instead of 172 nm as described above. Got.
[0054]
From the above, by diffusing hydrogen (H 2) or deuterium (D 2) into the silica-based optical waveguide and irradiating the excimer lamp light 33 from the excimer lamp 31, the signal light absorption characteristics of the optical waveguide are obtained. It was confirmed that it can be used as an optical attenuator.
[0055]
【The invention's effect】
According to the first aspect of the present invention, deuterium is pressurized and diffused inside the silica-based optical waveguide, and the silica-based optical waveguide into which deuterium is diffused is irradiated with incoherent ultraviolet light from a light source. Then, after increasing the OD group in the quartz optical waveguide, the quartz optical waveguide is heated to release residual deuterium to the outside, and the transmitted light is absorbed by the increased OD group in the quartz optical waveguide. This attenuation can contribute to the manufacture of an optical attenuator capable of attenuating signal light, and can easily be mass-produced.
[0056]
According to the second aspect of the present invention, since the light source is an excimer lamp that emits ultraviolet light having a wavelength of 172 nm, an excimer lamp having a wavelength that is commercially available can be used, and mass production can be easily performed. Is possible.
[0057]
According to the third aspect of the present invention, since the light source is an excimer lamp that emits ultraviolet light having a wavelength of 222 nm, an excimer lamp having a wavelength that is commercially available can be used, and mass production can be easily performed. Is possible.
[0058]
According to the fourth aspect of the present invention, the silica-based optical waveguide includes at least one of germanium, phosphorus, and boron as an additive material for increasing the absorption of the signal light, thereby absorbing the signal light. Can be increased.
[0059]
According to the fifth aspect of the present invention, since the intensity of the ultraviolet light emitted from the light source is adjusted by the filter and reaches the silica-based optical waveguide, the O D in accordance with the intensity of the ultraviolet light within the silica-based optical waveguide. The degree of group increase can be adjusted.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a configuration of a fiber-type optical attenuator 11 manufactured by an optical component manufacturing method according to the present invention.
FIG. 2 is a manufacturing process flow of the optical attenuator 11;
3 is an explanatory diagram of a process P1 for manufacturing the optical attenuator 11. FIG.
4 is an explanatory diagram of a process P2 for manufacturing the optical attenuator 11. FIG.
FIG. 5 is an explanatory diagram of a process P3 for manufacturing the optical attenuator 11.
FIG. 6 is a graph showing wavelength loss characteristics of the optical fiber 13 after being irradiated with excimer lamp light for 10 minutes.
7 is a graph showing the excimer lamp light irradiation time and the transmission loss characteristics of the optical fiber 13. FIG.
FIGS. 8A and 8B are diagrams showing a conventional method in which a metal ion is added to the core of an optical fiber to absorb signal light, and FIG. 8B is a diagram showing a metal thin film at a position where the optical fiber is cut. It is a figure which shows the method of inserting and absorbing signal light, (c) is a figure which shows the method of heating a part of optical fiber at high temperature, enlarging a core diameter, and scattering signal light, (d) is a figure. It is a figure which shows the method which forms FBG in the core of an optical fiber, reflects the signal light of a specific wavelength, and attenuates transmitted light.
FIG. 9 is a graph showing gain characteristics when a conventional optical component is applied to a gain equalizing filter of an optical amplifier.
FIG. 10 is a graph showing gain characteristics of an optical amplifier after multistage relaying.
FIG. 11 is a graph showing loss characteristics of an optical attenuator after multistage relaying.
FIG. 12 is a graph showing that the gain is flat using an optical attenuator having a loss slope equal to the accumulated gain slope after multi-stage relaying.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Optical attenuator 13 Optical fiber 15a, 15b Cover 21 High pressure vessel 27 Core 29a, 29b Clad 31 Excimer lamp 33 Excimer lamp light 35 Intensity adjustment filter 41 Oven

Claims (5)

A diffusion process in which deuterium is pressurized and diffused into the silica-based optical waveguide;
An irradiation step of irradiating the silica-based optical waveguide in which deuterium is diffused by the diffusion step with incoherent ultraviolet light from a light source, and increasing an OD group in the silica-based optical waveguide;
A heating step of heating the quartz optical waveguide after the irradiation step to release deuterium remaining to the outside;
A method of manufacturing an optical attenuator, wherein signal light is absorbed and attenuated by an increased OD group in the quartz optical waveguide. The light source is
2. The method of manufacturing an optical attenuator according to claim 1, comprising an excimer lamp that emits ultraviolet light having a wavelength of 172 nm. The light source is
2. The method of manufacturing an optical attenuator according to claim 1, comprising an excimer lamp that emits ultraviolet light having a wavelength of 222 nm. The silica-based optical waveguide is
3. The method of manufacturing an optical attenuator according to claim 2 , wherein at least one of germanium, phosphorus, and boron is included as an additive material for increasing absorption of signal light. Between the light source and the silica-based optical waveguide,
3. The method of manufacturing an optical attenuator according to claim 2, further comprising a dimming step of inserting a filter for adjusting the intensity of ultraviolet light.

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