JPH09211245A - Production of waveguide type diffraction grating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a waveguide type diffraction grating which enhances stable reflectance for the component of light of specified wavelength. SOLUTION: An optical fiber 10 is arranged in a pressure container, into which hydrogen (H2 ) gas is introduced while the container is controlled to <=80 deg.C with 20 to 400atm of hydrogen pressure. Then a specified region of the core of the optical fiber 10 is irradiated with UV rays to form a diffraction grating 13 by changing the refractive index. Then the optical fiber 10 with the diffraction grating 13 formed is left in a thermostat having <=60 deg.C inner atmosphere which does not substantially contain hydrogen so as to diffuse hydrogen remaining in the optical fiber 10 from the optical fiber 10 while reaction of hydrogen is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a waveguide type diffraction grating in which a refractive index of a core portion of an optical waveguide is periodically changed along an optical axis to form a diffraction grating.

[0002]

2. Description of the Related Art In recent years, with the progress of optical fiber communication technology, the complexity of networks and the multiplexing of signal wavelengths have progressed, and the system configuration is becoming more sophisticated. In such an optical communication system, the importance of optical circuit elements is increasing.

As one of the general constitutions of optical circuit elements, the fiber type element is small in size and has a small insertion loss.
It has advantages such as easy connection with an optical fiber. A fiber type filter is known as such a fiber type element.

[0004] Recently, it has been well known that a silica-based optical fiber doped with germanium oxide in the core changes the refractive index of the core by irradiation with ultraviolet light.
An optical fiber type diffraction grating has been researched and developed as a fiber type filter utilizing such a light induced refractive index change.

This optical fiber type diffraction grating reflects a light component of a specific wavelength in the light traveling in the optical fiber. Generally, when the ultraviolet light is radiated, the refractive index of the core portion of the optical fiber is the optical axis. It is manufactured by forming periodically varying regions along the. In this manufacturing method,
There is an advantage that the fiber type diffraction grating can be manufactured with high productivity.

In such a fiber type diffraction grating, the reflectance R is an important characteristic, and the reflectance R is the grating length (the length of the region in which the refractive index of the core portion periodically changes along the optical axis). And the amount of light-induced change in the refractive index. This relationship is expressed as R = tanh ² (LπΔn / λ _R ), where R: reflectance L: grating length Δn: photoinduced change in refractive index λ _R : reflection wavelength.

[0007]

It is known that the change in the refractive index due to ultraviolet light irradiation is caused by glass defects related to germanium existing in the glass of the core portion. However, since the number of glass defects in a glass optical fiber in which a core portion is simply doped with germanium oxide as in the related art is small, the refractive index change Δn is small even when irradiated with ultraviolet light,
Therefore, as is clear from the above equation, the reflectance is low. Specifically, the change in the refractive index of the core portion due to the irradiation of ultraviolet light is about 10 ⁻⁵ , and the reflectance is a few percent, which is too small.

In order to increase the reflectance, there is also a method of increasing the grating length L as shown by the above equation, but when irradiating the ultraviolet laser beam, the laser beam is required to have high uniformity, and therefore, In addition, there is a problem that the optical system for irradiating ultraviolet light becomes complicated. Also,
Since there are few glass defects, there is a problem that the rate of change of the refractive index due to the irradiation of ultraviolet light is slow, and if an attempt is made to increase the reflectance, the irradiation time becomes long and the productivity decreases.

A method is known in which hydrogen is added to the core of an optical fiber in order to increase the reflectance and increase the amount of change in the refractive index with respect to the irradiation light amount of ultraviolet light.

When ultraviolet light is applied to a predetermined region of the core portion of the optical fiber after hydrogenation, the amount of change in the refractive index increases and the reflectance increases, but the reflectance decreases during subsequent use. In addition, there is a problem that the reflectance decreases during use.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for easily and stably manufacturing a waveguide type diffraction grating having a high reflectance with high productivity. And

[0012]

According to a first aspect of the present invention, there is provided a method of manufacturing a waveguide type diffraction grating, comprising: (i) a first step of adding hydrogen to the core portion of the optical waveguide; and (ii) a core portion of the optical waveguide. A second step of irradiating a predetermined region of ultraviolet light with ultraviolet light to change the refractive index;
ii) The optical waveguide in which the refractive index of the core portion in the predetermined region is changed,
And a third step of leaving it in a substantially hydrogen-free atmosphere at a constant temperature of 60 ° C. or less.

Here, the addition of hydrogen to the optical waveguide in the first step is preferably carried out at an atmospheric temperature of 80 ° C. or lower and a hydrogen pressure of 20 atm or higher and 400 atm or lower. .

Further, it is practical that the third step is carried out in an air atmosphere or a nitrogen atmosphere.

Further, the third step may be characterized in that the optical waveguide is left to stand until the hydrogen concentration in the core portion of the optical waveguide becomes 1000 ppm or less.

In the method of manufacturing the waveguide type diffraction grating according to the first aspect, first, hydrogen is added to the core portion of the optical waveguide (first step). The addition of hydrogen to this optical waveguide can be carried out by a method of reducing the optical waveguide in a hydrogen atmosphere.

In this case, germanium oxide (GeO ₂ ) doped in the optical waveguide is easily reduced, and Ge
A phenomenon occurs in which oxygen bound to is partially removed. If Ge with some of the bound oxygen removed is bound to each other, oxygen-defective defects will newly occur, and oxygen-defective defects in the core portion of the optical waveguide will increase, causing a change in the refractive index due to irradiation with ultraviolet light. Will increase.

That is, quartz (S
io ₂ ) and germanium oxide (GeO ₂ ) doped therein are easily reduced as a whole, and Ge and Si
It is presumed that a phenomenon occurs in which oxygen bound to is partially removed. Ge and Si with some of the bound oxygen removed
Are bonded to each other, a neutral oxygen mono-vacancy such as Si—Ge or Ge—Ge, that is, an oxygen deficiency type defect is newly generated.

The optical waveguide to be reduced in the hydrogen atmosphere does not have to be a bare optical waveguide, and may be a resin-coated optical waveguide. In such a case, hydrogen can be added to the core portion of the optical waveguide by using the optical waveguide formed by applying the resin coating during drawing as it is.

Hydrogen is preferably added to the optical cable in the first step at an atmospheric temperature of 80 ° C. or lower and a hydrogen pressure of 20 atm or more and 400 atm or less.

Hydrogen in the optical waveguide also reacts with Ge by heat to form Ge-OH. This reaction inhibits the Ge-OH formation reaction due to ultraviolet irradiation.

In the case where the addition of hydrogen to the optical waveguide in the first step is a reduction treatment step in a hydrogen atmosphere, the higher the ambient temperature, the faster the diffusion rate of hydrogen and the shorter the treatment time. Since the added concentration is lowered, the effect of increasing the refractive index by irradiation with ultraviolet light is reduced.

Hydrogen in the optical waveguide also reacts with Ge by heat to form Ge-OH. This reaction is
It inhibits the Ge-OH formation reaction by UV irradiation. From this point of view, too high a processing temperature is not preferable.

According to the knowledge of the present inventor, the processing temperature is 80
It is preferable that the temperature is not higher than ° C.

When the hydrogen pressure is 20 atm or less, the effect of adding hydrogen is substantially insignificant, and when it is 100 atm or less, the effect of adding hydrogen is small. Then, as the hydrogen pressure is further increased, the effect of hydrogen addition is improved.
When the pressure is higher than 00 atm, the effect is gradually saturated, and when the pressure is higher than 400 atm, the effect due to the increase in hydrogen pressure is not observed.

Next, a predetermined region of the core portion of the hydrogen-doped optical waveguide is irradiated with ultraviolet light to change the refractive index (second step).

In a quartz glass optical waveguide doped with germanium oxide, the mechanism of the change in refractive index due to irradiation with ultraviolet light has not been completely clarified. However, as an important cause, an oxygen deficiency type defect related to germanium is considered, and such a defect is S
Neutral oxygen mono-pores such as i-Ge or Ge-Ge are envisioned. For the mechanism of such a change in the refractive index, refer to the literature "1993 IEICE Spring Conference, C-24.
3, pp. 4-279 ”and the like.

The inventor of the present application believes that the refractive index change due to ultraviolet light irradiation will be increased by increasing the number of oxygen deficiency type defects, which are usually present in a small amount in a germanium oxide-doped silica-based optical waveguide. Estimated. Then, it was found that reduction treatment of the optical waveguide in a hydrogen atmosphere is effective for increasing the number of germanium-related oxygen-deficient defects existing in the optical waveguide.

Hydrogen is added to the optical waveguide by reducing the optical cable in a hydrogen atmosphere. According to the knowledge of the present inventors, when the optical waveguide to which hydrogen is added is irradiated with ultraviolet light, the added hydrogen reacts with germanium and oxygen in the optical waveguide material to form a new bond of Ge—OH. Form and these bonds enhance the refractive index change.

It is easy to irradiate the ultraviolet light by irradiating the predetermined region of the core portion with the interference fringes generated by the interference of the ultraviolet light. The interference fringes of the ultraviolet light are obtained by irradiating one of the branched ultraviolet light at a first angle with respect to the axial direction of the core portion and the other at a second angle which is a complementary angle of the first angle to a predetermined region. It is suitable to be formed by. According to this holographic method, the change in the refractive index of the core portion occurs at a cycle corresponding to the incident angles of these two branched lights. Further, it is appropriate that the interference fringes of the ultraviolet light are formed by irradiating a phase grating having a grating arranged in a predetermined cycle with the ultraviolet light at a predetermined angle with respect to the plane direction of the phase grating. According to this phase grating method, the change in the refractive index of the core portion occurs at a period corresponding to the grating arrangement of the phase grating.

According to the experiments by the present inventors, when 10000 ppm of hydrogen is added to the core portion of the optical waveguide, the refractive index change is 1 when the core portion contains sufficient Ge.
It reaches 0 ^-3, and the reflectance as a diffraction grating can reach almost 100%.

Then, the optical waveguide in which the refractive index of the core portion in the predetermined region is changed is left to stand in an atmosphere substantially free of hydrogen at a constant temperature of 60 ° C. or lower (third step).

Hydrogen is consumed in the portion irradiated with ultraviolet light in the second step, but hydrogen remains in other regions. Therefore, after writing the diffraction grating, hydrogen remains in most of the region. Although such hydrogen gradually decreases due to diffusion, it reacts with heat depending on the storage environment temperature and the use environment temperature, and Ge
OH such as -OH is generated, which adversely affects the characteristics of the diffraction grating.

As a result of earnest research, the present inventor has found that the OH generation reaction due to the heat of the residual hydrogen causes the instability of the characteristics of the waveguide type diffraction grating using the hydrogenated waveguide. .

Therefore, in the third step, if the optical waveguide on which the diffraction grating has been written up to the second step is left as it is, that is, if the coating is peeled off in the second step, the optical waveguide is heated. In order to promote the diffusion of hydrogen, the peeled state is left as it is without any reinforcement or the like, and the hydrogen is allowed to stand in a substantially hydrogen-free atmosphere at a constant temperature.

According to the findings obtained by the inventor of the present invention,
When the ambient temperature of the optical waveguide is 60 ° C. or lower, OH generation does not substantially affect the characteristics of the diffraction grating. Further, unless the temperature is constant, the final characteristics of the diffraction grating are not uniform. Therefore, in the third step, it is preferable to use a constant temperature bath.

As an atmosphere containing substantially no hydrogen,
It can be atmospheric or nitrogen atmosphere,
By adopting such an atmosphere, an atmosphere containing substantially no hydrogen can be easily realized.

Further, according to the knowledge obtained by the inventor as a result of the research, if the residual hydrogen concentration in the core portion of the optical waveguide is set to 1000 ppm or less in the third step, the subsequent storage temperature and operating temperature are concerned. However, the adverse effect of the generated OH on the characteristics of the diffraction grating can be substantially ignored.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method for manufacturing a waveguide type diffraction grating of the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Further, the dimensional ratios in the drawings do not always match those described.

In the method of manufacturing the waveguide type diffraction grating of this embodiment, first, an optical fiber is prepared, and the optical fiber is heated in a hydrogen atmosphere for reduction treatment.

Specifically, as shown in FIG. 1, the optical fiber 10 is installed in the pressure vessel 20, and hydrogen (H ₂ ) gas is passed from the valve 21 side toward the valve 22 as an air flow, while being illustrated. The temperature of the pressure vessel 20 is set with a heater that does not. At this time, the flow rate of hydrogen gas is controlled by the valves 21 and 2
Adjusted by opening and closing 2.

The optical fiber 10 is an ordinary silica-based optical fiber containing germanium oxide (GeO ₂ ) in its core portion, or may be an optical fiber core wire having a secondary coating. The atmosphere has a hydrogen pressure of 20 to 400 atm, and the atmosphere temperature is set to 80 ° C or lower.

The atmosphere temperature is set to 80 ° C. or lower because
This is because when the atmospheric temperature is high, the diffusion rate of hydrogen is high and the processing time is short, but the concentration of addition is low, and the effect of increasing the refractive index by irradiation with ultraviolet light is reduced. Hydrogen in the optical fiber 10 also reacts with Ge by heat to form Ge-OH. This reaction inhibits the Ge-OH formation reaction due to ultraviolet irradiation. From this point of view, it is not preferable that the treatment temperature exceeds 80 ° C.

The hydrogen pressure is set to 20 atm or higher because the effect of hydrogen addition is not substantially obtained when the hydrogen pressure is lower than 20 atm. From the viewpoint of the effect of hydrogen addition, the hydrogen pressure is preferably 100 atm or higher.

The hydrogen pressure of 400 atm or less is 4
This is because the effect of hydrogenation is saturated when the pressure exceeds 00 atm. The tendency of these effects to become saturated becomes apparent when the hydrogen pressure exceeds 300 atm.

According to such a hydrogen adding step, the hydrogen added to the optical fiber 10 facilitates the reduction of the germanium oxide doped in the core of the optical fiber 10, and the oxygen bonded to Ge or Si is reduced. The phenomenon that parts are removed occurs. Ge or S with some bound oxygen removed
If i is bonded to each other, oxygen deficiency type defects are newly generated, and the number of oxygen deficiency type defects, which are usually few in the core portion of the optical cable, increases.

Next, ultraviolet light interference fringes are applied to a predetermined region of the core portion in the optical fiber 10 processed in the hydrogenation process.

FIG. 2 is an illustration of irradiation of ultraviolet light interference fringes by the holographic method. As shown in FIG. 2, the ultraviolet light emitted from the light source 30 is caused to interfere with each other so as to generate the interference space 50 by using the interference mechanism 40.
The optical fiber 10 is installed at 0. The light source 30 is SHG
(Harmonic Wave Generator) An argon laser, a KrF excimer laser, or the like, which emits coherent ultraviolet light having a predetermined wavelength. The interference mechanism 40 includes a beam splitter 41 and mirrors 42 and 43. The beam splitter 41 splits the ultraviolet light from the light source 30 into two split lights. The mirrors 42 and 43 are the beam splitter 41.
From the optical fiber 10 are reflected and are made incident at predetermined angles θ ₁ and θ ₂ with respect to the axial direction of the optical fiber 10 to interfere with each other as coplanar beams. The optical fiber 10 is composed of a clad portion 11 and a core portion 12 made of silica glass. The core portion 12 is doped with germanium oxide as described above, and has a higher refractive index than the cladding portion 11. The incident angle θ of the two split lights
₁ and θ ₂ are complementary angles to each other, and their sum (θ ₁ + θ
₂ ) becomes 180 °.

According to such a process, the optical fiber 10
Since it is irradiated with ultraviolet light of a predetermined wavelength, the refractive index of the exposed region in the core portion 12 doped with germanium oxide changes. At present, the mechanism of such a change in the refractive index by irradiation with ultraviolet light has not been completely clarified. However, the Kramers-Kronig mechanism, the dipole model, the compression model, and the like have been generally proposed to explain this. Here, description will be given based on the Kramers-Kronig mechanism.

The core portion 12 in the optical fiber 10 has Ge
There are usually a few oxygen-deficient defects associated with. Here, when the defect is represented by Ge-Si neutral oxygen mono-vacancy, the defect is converted by Ge irradiation by Ge-Si → Ge · + Si ⁺ + e ⁻ (1). The electrons emitted by this reaction are trapped in Ge located around the converted defects, so that the light absorption characteristics of the core portion 12 change. According to the absorption spectrum of such a defect, it is confirmed that a peak appears around a wavelength of 240 to 250 nm before irradiation with ultraviolet light, but the peak transits around a wavelength of 210 nm and around 280 nm after irradiation with ultraviolet light. It is believed that this transition changes the refractive index of the core. In addition,
Based on the well-known Kramers-Kronig relational expression, the value of the change in the refractive index in the core portion 12 estimated from the change in the absorption spectrum of the defect is in good agreement with the value of the change in the refractive index calculated from the measured value of the reflectance.

In the core portion 12 of the optical fiber 10 which has been hydrogenated and reduced in the hydrogenation step, as described above, oxygen deficiency type defects, which usually exist in small numbers, are increased. The refractive index change becomes large. In addition to this, when the core is irradiated with ultraviolet light,
Ge or Si from which oxygen is removed, or normal Ge-
A bond such as O—Si reacts with hydrogen added to the optical cable to form Ge—H, Ge—OH, Si—H, Si.
The bond —OH is formed. The present inventor speculates that these bonds form a new light absorption band, thereby increasing the change in the refractive index due to the irradiation of ultraviolet light. Therefore,
According to the method of the present invention, the effect due to the increase of oxygen deficiency type defects and the new bond (Ge) generated by the reaction of added hydrogen
-H, etc.), the refractive index change in the exposure region of ultraviolet light increases to about 10 ⁻⁴ to 10 ⁻³ .

In the holographic method of FIG. 2, two coherent ultraviolet rays are made incident at angles θ ₁ and θ ₂ (= 180 ° −θ ₁ ) with respect to the axial direction of the optical fiber 10 and interfere with each other. Therefore, the incident angle θ (= 90 ° −θ ₁ ) of the coherent ultraviolet light with respect to the radial direction of the optical fiber 10
And the wavelength λ of the ultraviolet light, the interval Λ of the interference fringes in the interference space 50 is Λ = λ / (2sinθ) (2). Therefore, in the exposed region of the core portion 12, regions having different refractive indices are arranged in the axial direction of the optical fiber 10 with the interval 干 渉 of the interference fringes as a period, so that the grating 13 is formed.

Based on the Bragg diffraction condition, the core portion 12
The reflection wavelength λ _R of this fiber type diffraction grating is λ _R = 2nΛ = λn / sin θ (3) by using the refractive index n of γ and the period Λ of the grating 13. Further, using the length L of the grating 13 and the refractive index difference Δn, the reflectance R of this fiber type diffraction grating is R = tanh ² (LπΔn / λ _R ) (4). Therefore, in the core portion 12 of the optical fiber 10, since the grating 13 is formed with a large change in the refractive index of about 10 ⁻⁴ to 10 ⁻³ , the reflectance of the reflection wavelength λ _R is 100.
Reaches a value close to%.

In such a holographic method, a laser having good coherence is required as the light source 30. In addition, highly accurate position adjustment and stability are required.

FIG. 3 is an illustration of irradiation of ultraviolet light interference fringes by the phase grating method. As shown in FIG. 3, the optical fiber 1
0 is installed adjacent to the phase grating 60, and the ultraviolet light emitted from the light source 30 is incident at a predetermined angle θ with respect to the normal direction of the surface of the phase grating 60. The light source 30 is an SHG argon laser, a KrF excimer laser, or the like, which emits coherent ultraviolet light having a predetermined wavelength. The phase grating 60 is formed by arranging gratings at a predetermined cycle. The optical fiber 10 has a clad portion 11 made of silica glass.
And the core portion 12. The core portion 12 is doped with germanium oxide as described above, and has a higher refractive index than the cladding portion 11.

According to the phase grating method of FIG. 3, the optical fiber 1
Since 0 is irradiated with ultraviolet light of a predetermined wavelength, the refractive index of the exposed region in the core portion 12 doped with germanium oxide changes. At present, the mechanism of such a change in the refractive index by irradiation with ultraviolet light has not been completely clarified. However, the core portion 1 of the fiber 10 is affected by this change in refractive index.
It is generally presumed that a Ge-related oxygen-deficient defect, which is usually present in 2 in a small amount, is involved.

In the core portion 12 of the optical fiber 10 which has been hydrogenated and reduced in the hydrogenation step, oxygen deficiency type defects, which are usually small, are increased, so that the change of the refractive index in the exposure region of the ultraviolet light is changed. growing.

Further, ultraviolet light is irradiated at an angle θ with respect to the normal direction of the surface of the phase grating 60 in which the gratings are arranged at a predetermined interval Λ ', and they interfere with each other. Therefore, the interval Λ of the interference fringes in the exposure area of the core portion 12 is Λ = Λ ′ (5). Therefore, in the exposed region of the core portion 12, regions having different refractive indices are arranged in the axial direction of the optical fiber 10 with the interval 干 渉 of the interference fringes as a period, so that the grating 13 is formed.

Using the refractive index n of the core 12 and the period Λ of the grating 13 based on the well-known Bragg diffraction condition, the reflection wavelength λ _R of this fiber type diffraction grating is λ _R = 2nΛ = 2nΛ '(6 ). Further, using the length L of the grating 13 and the refractive index difference Δn, the reflectance R of this fiber type diffraction grating is as shown in the above-mentioned formula (4). Therefore, the optical fiber 10
In the core portion 12, the grating 13 is formed with a large change in the refractive index of about 10 ⁻⁴ to 10 ^−3, so that the reflectance of the reflection wavelength λ _R reaches a value close to 100%.

According to such a phase grating method, the conditions for position adjustment and stability required for the above-mentioned holographic method are alleviated. Moreover, since the lattice period can be freely selected by the ordinary lithography technique or chemical etching, a complicated shape can be realized.

Then, the optical fiber 10 on which the diffraction grating 13 is formed is left to stand in an atmosphere substantially free of hydrogen at a constant temperature of 60 ° C. or lower.

Specifically, as shown in FIG. 4, the constant temperature bath 2
The optical fiber 10 is installed in the valve 5, and the inside of the constant temperature bath 25 such as a heater (not shown) is controlled to a constant temperature of 60 ° C. or lower while passing the atmosphere from the valve 26 side toward the valve 26 as an air flow. At this time, the flow rate of the atmosphere is adjusted by opening and closing the valves 26 and 27.

The atmosphere temperature is set to 60 ° C. or lower because
This is because if the ambient temperature is high, the OH generation reaction due to hydrogen remaining in the optical fiber 10 is promoted.

The pressure in the constant temperature bath 25 is not limited, but atmospheric pressure is practical.

The atmosphere inside the constant temperature bath 25 can be a nitrogen atmosphere.

The hydrogen concentration in the optical fiber 10 is 1
After leaving the optical fiber 10 in the constant temperature bath 25 until it becomes 000 ppm or less, the optical fiber 10 is taken out from the constant temperature bath 25. The extracted optical fiber 10 is reinforced and the like to obtain a fiber type diffraction grating.

The reflectance of the fiber type diffraction grating thus manufactured is measured as follows. FIG. 5 is a configuration diagram of a system for measuring the reflectance of the fiber type diffraction grating. As shown in FIG. 5, this system includes a light source 7
0, the optical fiber 10 and the optical spectrum analyzer 90 are optically coupled by an optical coupler 80.

The light source 70 is an ordinary light emitting diode or the like, and emits light containing a light component having a reflection wavelength λ _R in the optical fiber 10. The optical coupler 80 is a normal melt-stretch fiber coupler, which outputs the incident light from the light source 70 to the optical fiber 10 and outputs the reflected light from the optical fiber 10 to the optical spectrum analyzer 90. The optical spectrum analyzer 90 detects the relationship between the wavelength and the light intensity of the reflected light from the optical fiber 10. The open end of the optical fiber 10 is immersed in the matching oil 100. This matching oil 100 is a normal refractive index matching liquid and removes unnecessary reflected light components.

According to the system of FIG. 5, the light emitted from the light source 70 enters the optical fiber 10 via the optical coupler 80. In the optical fiber 10, the grating 13 formed on the core portion 12 reflects a light component having a specific wavelength. The light emitted from the optical fiber 10 is received by the optical spectrum analyzer 90 via the optical coupler 80. The optical spectrum analyzer 90 detects the reflection spectrum of the optical fiber 10, which is composed of wavelength and light intensity.

[0070]

EXAMPLES The present inventor manufactures a fiber type diffraction grating based on the above-described embodiment as follows,
The reflectance was measured.

First, an optical fiber having a germanium-doped core was placed in a pressure vessel having an atmosphere of hydrogen pressure of 200 atm and an internal temperature of 30 ° C. and subjected to hydrogenation treatment for 2 weeks.

Next, a diffraction grating was written with an excimer laser combined with a holographic interference system as shown in FIG. At this point, the reflectance was measured by the system shown in FIG. 5 and it was about 100%.

Next, the optical fiber in which the diffraction grating was written was left for 2 weeks in a thermostat in which the atmospheric temperature was circulated and the ambient temperature was 30 ° C.

With respect to the fiber type diffraction grating thus obtained, the reflectance was measured by the system shown in FIG. 5, and it was about 100%, and no change was observed thereafter.

When the hydrogen concentration of this fiber type diffraction grating was measured, the hydrogen concentration was about 100 ppm.

The present inventor manufactured a fiber type diffraction grating of the following comparative example and measured the reflectance in order to compare with the above example.

(Comparative Example 1) First, an optical fiber having a germanium-doped core was prepared under the hydrogen pressure of 20 as in the example.
It was placed in a pressure vessel having an atmosphere of 0 atmosphere and an internal temperature of 30 ° C., and subjected to hydrogenation treatment for 2 weeks.

Next, as in the embodiment, a diffraction grating was written by an excimer laser combined with a holographic interference system as shown in FIG. At this point, the reflectance was measured by the system shown in FIG. 5 and it was about 100%.

Next, the optical fiber in which the diffraction grating was written was left for 1 week in a thermostat in which the atmosphere was circulated and the ambient temperature was 80 ° C.

When the reflectance of the thus obtained fiber type diffraction grating was measured by the system shown in FIG. 5, the reflectance was lowered to about 80%. No change was observed after that.

When the hydrogen concentration of this fiber type diffraction grating was measured, the hydrogen concentration was about 50 ppm.

(Comparative Example 2) First, an optical fiber having a germanium-doped core was prepared at a hydrogen pressure of 20 as in the example.
It was placed in a pressure vessel having an atmosphere of 0 atmosphere and an internal temperature of 30 ° C., and subjected to hydrogenation treatment for 2 weeks.

Then, similarly to the embodiment, a diffraction grating was written by using an excimer laser combined with a holographic interference system as shown in FIG. At this point, the reflectance was measured by the system shown in FIG. 5 and it was about 100%.

Next, the optical fiber in which the diffraction grating was written was left for 5 days in a constant temperature chamber in which the atmosphere was circulated and the ambient temperature was 30 ° C.

When the reflectance of the fiber type diffraction grating thus obtained was measured by the system shown in FIG. 5, the reflectance was about 100%, but when it was subsequently used in an environment of 80 ° C., The reflectance gradually decreased to 70%.

Further, when the hydrogen concentration of the fiber type diffraction grating immediately after being taken out from the constant temperature bath was measured, the hydrogen concentration was about 1500 ppm.

The present invention is not limited to the above embodiment, but can be modified. For example, in the above embodiment, the optical fiber is subjected to the hydrogenation treatment and the grating is formed in a predetermined region of the optical fiber, but a thin film waveguide may be used as the optical waveguide other than the optical fiber. The thin film waveguide having the core portion covered with the lower clad layer and the upper clad layer may be subjected to hydrogenation treatment after the core portion is formed on the lower clad layer and before the upper clad layer is laminated. . After that, by irradiating with ultraviolet light to form a grating in a predetermined region of the core portion and then stacking an upper clad layer, a thin film waveguide type diffraction grating is obtained.

[0088]

As described above in detail, according to the method of manufacturing the waveguide type diffraction grating of the present invention, hydrogen is added to the core portion of the optical waveguide, and hydrogen is added to the predetermined region of the core portion of the optical waveguide. After irradiating with ultraviolet light to change the refractive index, the optical waveguide in which the refractive index of the core portion in the predetermined region is changed is left to stand in a substantially hydrogen-free atmosphere at a constant temperature of 60 ° C. or less, Since hydrogen is diffused to the outside of the waveguide while suppressing the reaction of hydrogen inside the waveguide, it is possible to manufacture an optical cable type diffraction grating with high reflectance easily, with high productivity, and stably. it can.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a hydrogenation process in a method for manufacturing a waveguide type diffraction grating according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a diffraction grating writing step (holographic method) in the method of manufacturing the waveguide type diffraction grating according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram of a diffraction grating writing step (phase grating method) in the method for manufacturing a waveguide type diffraction grating according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a hydrogen diffusion step in the method of manufacturing a waveguide type diffraction grating according to the embodiment of the present invention.

FIG. 5 is a configuration diagram showing a system for measuring reflectance in a waveguide type diffraction grating.

[Explanation of symbols]

10 ... Optical fiber, 11 ... Clad part, 12 ... Core part,
13 ... Diffraction grating, 20, 25 ... Pressure vessel 21, 22, 22
26, 27 ... Bulb, 30, 70 ... Light source, 40 ... Interference mechanism, 41 ... Beam splitter, 42, 43 ... Mirror, 5
0 ... Interference space, 60 ... Phase grating, 80 ... Optical coupler, 90
… Optical spectrum analyzer, 100… Matching oil.

Claims (4)

[Claims] 1. A first method for adding hydrogen to a core portion of an optical waveguide
The second step of irradiating a predetermined region of the core portion of the optical waveguide with ultraviolet light to change the refractive index, and the optical waveguide in which the refractive index of the core portion of the predetermined region is changed, And a third step of leaving it in a substantially hydrogen-free atmosphere at a constant temperature of ℃ or less, and a method of manufacturing a waveguide type diffraction grating. 2. The addition of hydrogen to the optical waveguide in the first step is performed at an atmospheric temperature of 80 ° C. or lower and a hydrogen pressure of 20 atm or more and 400 atm or less. The method for manufacturing a waveguide type diffraction grating according to claim 1. 3. The method for manufacturing a waveguide type diffraction grating according to claim 1, wherein the third step is performed in an air atmosphere or a nitrogen atmosphere. 4. The conductor according to claim 1, wherein the third step is a step of leaving the optical waveguide as it is until the hydrogen concentration of the core portion of the optical waveguide becomes 1000 ppm or less. Method of manufacturing waveguide diffraction grating.