JP2000155231A - Waveguide core film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a waveguide core film which can be used both as a normal waveguide core film stable against UV rays and as a grating core film having sensitivity to UV rays and showing large changes in the refractive index induced by light by depositing a waveguide core film by a specified method and heat treating the core film in an oxidative atmosphere as the posttreatment. SOLUTION: This waveguide core film consists of a quartz glass core film with addition of Ge, and the quartz glass core film with addition of Ge deposited by a CVD method on a substrate is heat treated in an oxidative atmosphere at a higher temp. than the temp. in the deposition process. Although an absorption band appears at 5.1 eV caused by oxygen-deficit defects of Ge in the initial waveguide core film Ias, such absorption band does not appear in the initial waveguide core film IIas. Therefore, the initial waveguide core film IIas is not an oxygen-deficit glass so that it is suitable to form a waveguide stable against UV rays.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a core film for a waveguide and a method for manufacturing the same. In particular, the present invention relates to a waveguide core film suitable for forming an optical element such as a grating using a photo-induced refractive index change, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing a waveguide core film, a CVD method (Chemical Vapor Deposition; Chemical Vapor D) has been used.
eposition) or FHD method (flame deposition method; Flame Hyd)
It is known that a waveguide core film made of quartz glass is deposited on a silica substrate by rolysis deposition.
Here, the CVD method is a method in which a gas having a composition to be deposited as a waveguide core film is decomposed by heat or plasma and deposited on a substrate. The FHD method is an application of the VAD technique, which is a method of manufacturing an optical fiber, in which porous glass is sprayed on a substrate and sintered. Usually, by etching the waveguide core film or the like, the core portion required as a waveguide is cut out only by performing an etching process or the like, and a cladding layer or the like is formed on the core portion to form a waveguide. Used. In addition, Ge (germanium) is usually added to the above-described waveguide core film in order to increase the refractive index of the core portion and confine light in the core portion. The amount of Ge added to the ordinary waveguide core film is set in the range of about 3.5 to about 10 mol% in order to obtain a high refractive index for sufficiently confining light and to suppress transmission loss. Have been.

On the other hand, by irradiating the Ge-doped quartz glass core film with ultraviolet light, for example, a grating that is a periodic refractive index modulation fringe is written, and this grating is reflected, for example, to reflect a specific wavelength. Techniques for use as optical elements such as filters have been developed. The waveguide on which these optical elements are formed is interposed in the middle of a normal waveguide for optical communication, and is used for various light controls in optical communication. In the waveguide core film to which Ge is added as described above, the photon energy (Photon Energ
The absorption characteristic determined by the relationship between y) and the absorption coefficient or the absorbance of light (absorption coefficient) is such that an absorption band having a peak at approximately 5.1 eV is generated due to the Ge added as described above ( For example, H.Hos
ono et al, Narure and origin of the 5-eV band in S
iO ₂ : GeO ₂ glasses, PHYSICAL REVIEW B, Vol.46, No.1
8, pp 11445-11451, November 1992). For this reason, by irradiating ultraviolet light having a wavelength corresponding to the above-mentioned absorption band, refractive index modulation is caused in the waveguide core portion. In addition, the refractive index modulation may be caused by Ge-related paramagnetic defects, particularly GeE'center (E prime center of Ge;
One oxygen is removed from the original four-coordinate structure in which oxygen is bonded to each of the four bonding hands centered on Ge to form a three-coordinate structure, leaving one Ge electron hand. (KDSimmons
et al, Correlation of defect centers with a wavele
ngth-dependent photosensitive response in germania
-doped silica optical fibers, OPTICS LETTERS, Vol.
16, No. 3, pp 141-143, February 1991). 5.1 eV
It is believed that the more (higher) the number of defects (defect concentration) having an absorption peak in the Ge, the more this Ge-related paramagnetic defect is induced by ultraviolet light irradiation, and as a result, the change in the photoinduced refractive index becomes larger. Have been.

However, in order to write a grating or the like on a Ge-doped quartz glass core film, only by adding Ge (about 3.5 mol% to about 10 mol%) in the above-described ordinary waveguide core film, Since a sufficient light-induced refractive index change (sometimes referred to as photosensitivity) cannot be obtained, the following method is conventionally known to increase the light-induced refractive index change. That is, for example, a method of adding another element such as B (boron) in addition to the above Ge (Tetsuro Komukai et al., “High Sensitivity of Optical Fiber for Bragg Grating”), IEICE Electronics Society Conference, C -139, pp139, 1996) or a method of adding hydrogen to a waveguide core film to which Ge has been added in a later step (see, for example, JP-A-10-82919).

[0005]

However, the above Ge
According to the method of adding other elements in addition to the above, the light-induced refractive index change type waveguide core film and the normal waveguide core film must be separately formed, that is, it is necessary to deposit each in a different process. . The ordinary waveguide core film is stable without causing a change in the refractive index even when receiving ultraviolet light, that is, even when irradiated with ultraviolet light, the above-mentioned defects do not occur and the ultraviolet to visible to red Good transmittance is required over the entire outside wavelength range, and a normal waveguide core film is manufactured with such a target as a target. On the other hand, a waveguide core film in which an optical element such as a grating is formed by a light-induced refractive index change has a characteristic opposite to that of the above-described ordinary waveguide core film, that is, although transmission loss is high for each of the above wavelengths, Those which are easy to induce a change in the refractive index upon irradiation with ultraviolet light are preferable.
Therefore, it is necessary to manufacture the photo-induced refractive index change type waveguide core film using a special material different from a normal waveguide core film, which requires a lot of labor and increases the manufacturing efficiency. Low.

Further, according to the above-described method of adding hydrogen for increasing the photo-induced refractive index change, the hydrogenation treatment is usually carried out for several weeks by placing the core in a closed container filled with high-pressure hydrogen. Since it is carried out by leaving it unattended, a large processing time is required in addition to the equipment for this addition processing.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a normal waveguide core film and a light-induced refractive index change type core film with high efficiency. It is an object to provide a core film and a waveguide obtained by such a manufacturing method. In particular,
Without adding an element different from Ge or adding hydrogen by post-processing to increase the photoinduced refractive index change,
By performing post-processing on the waveguide core film deposited in the same process, even a normal waveguide core film that is stable against ultraviolet light can be used as a grating core that is sensitive to ultraviolet light and has a large photoinduced refractive index change. An object of the present invention is to provide a waveguide core film which can be applied to any of the films and a method for manufacturing the same.

[0008]

In order to achieve the above object, the present invention provides a method for post-processing a waveguide core film deposited by a specific method in an oxidizing atmosphere (in the presence of oxygen).
Alternatively, by performing heat treatment in a non-oxidizing atmosphere, the state of a Ge-related defect that absorbs ultraviolet light changes, and it is found that the absorption peak of an absorption band caused by the defect decreases or increases. It was done.

Specifically, the waveguide core film according to the first invention is a waveguide core film made of a silica-based glass core film doped with Ge, and is a Ge-doped core film deposited on a substrate by a CVD method. The quartz-based glass core film is subjected to a heat treatment in an oxidizing atmosphere (for example, in the presence of oxygen such as an air atmosphere) at a temperature higher than at least the deposition time.

[0010] A second invention relates to a method of manufacturing a waveguide core film according to the first invention, wherein the method comprises manufacturing a silica-based glass core film to which Ge is added. Depositing a quartz-based glass core film on a substrate while adding Ge by CVD, and, after the depositing step, subjecting the quartz-based glass core film to an oxidizing atmosphere (for example, in the presence of oxygen such as an air atmosphere). And performing a heat treatment at a higher temperature than at least the deposition step.
The deposition step may be performed in an oxygen-deficient atmosphere.

Here, the deposition of the Ge-doped quartz glass core film by the CVD method is performed, for example, at a temperature higher than 700.degree.
When the heat treatment is performed in a temperature range not exceeding ℃, the heat treatment may be performed at a temperature of 800 ℃ or more. Further, “in an oxidizing atmosphere or in the presence of oxygen” means that the atmosphere is not an oxygen-deficient atmosphere, and as is clear from the description of the embodiment described below, the Ge element of the oxygen-deficient defect is oxidized (bonding to oxygen) Formation) refers to an atmosphere that can supply as much oxygen as possible. The oxygen partial pressure is preferably about 0.1 atm or more, more preferably about 0.5 atm or more (however, substantially no reducing hydrogen gas is contained). Although there is no particular upper limit for the oxygen partial pressure and the total pressure of the atmosphere, for simplicity,
It is preferably at most atmospheric pressure (1 atm).

Further, the waveguide core film according to the third invention is a waveguide core film made of a Ge-doped quartz glass core film, wherein the Ge-doped quartz core film is deposited on a substrate by a CVD method. The glass core film is heat-treated in a non-oxidizing atmosphere at a temperature higher than at least the deposition time. A grating may be formed in the waveguide core film that has been heat-treated in a non-oxidizing atmosphere.

A fourth invention relates to the method of manufacturing a waveguide core film according to the third invention, wherein the method is for manufacturing a silica-based glass core film to which Ge is added. Depositing a quartz-based glass core film on a substrate while adding Ge by a CVD method, and after the depositing step, applying a temperature higher than at least the deposition step to the quartz-based glass core film in a non-oxidizing atmosphere. And performing a heat treatment. Here, the non-oxidizing atmosphere in the heat treatment step may be an inert gas atmosphere.
The method may further include a step of forming a grating by irradiating at least a part of the quartz-based glass core film that has been subjected to the heat treatment in the non-oxidizing atmosphere with ultraviolet light.

In the case of the first or second invention, the CV
When heat treatment (or thermal annealing) is performed on an as-grown waveguide core film (hereinafter, referred to as an initial waveguide core film) deposited by the method D in an oxidizing atmosphere, the heat treatment time elapses. Reduce the absorption peak around 5.1 eV. That is, as the heat treatment time elapses, the absorption intensity of the irradiated ultraviolet light decreases, and the change in the refractive index due to the irradiation of the ultraviolet light decreases. In other words, the above-described heat treatment allows a stable waveguide core film having no change in refractive index even when irradiated with ultraviolet light, that is, a normal waveguide core film, not for a grating. .
This is because oxygen is taken into the initial waveguide core film when the initial waveguide core film is subjected to a heat treatment in an oxidizing atmosphere, and the oxygen is bonded to the Ge-related defect to reduce the defect. Can be

[0015] The initial waveguide core film is treated with C in an oxygen-deficient atmosphere.
If deposited by the VD method, an initial waveguide core film containing many oxygen-deficient defects can be obtained. The initial waveguide core film thus obtained is exposed to the above Ge by irradiation with ultraviolet light.
Since E'center increases, it has a large photoinduced refractive index change, and can be suitably used for writing an optical element (grating or the like). By subjecting this initial waveguide core film to a heat treatment in the above-described oxidizing atmosphere as a post-treatment, a waveguide core film suitable for use as a normal waveguide core film having a small refractive index change due to ultraviolet light irradiation is obtained. can get.

Therefore, it is possible to manufacture the original photoinduced refractive index change type waveguide core film without adding an element different from Ge and adding hydrogen by post-processing.
On the other hand, by performing the above-mentioned post-treatment on the initial waveguide core film manufactured in the same process (such as the conditions of the CVD method) as the light-induced refractive index change type waveguide core film for forming the optical element,
It is also possible to manufacture a normal waveguide core film that is stable against ultraviolet light.

In the case of the third or fourth invention, the CV
When the initial waveguide core film deposited by the method D is subjected to a heat treatment in a non-oxidizing atmosphere, the absorption peak near 5.1 eV due to Ge increases with the elapse of the heat treatment time. That is, as the heat treatment time elapses, the degree of absorption of the irradiated ultraviolet light increases, and the degree of change in the refractive index due to the irradiation of the ultraviolet light increases. In other words, the above heat treatment makes it possible to obtain a photoinduced refractive index change type waveguide core film suitable for forming an optical element such as a grating having a large change in refractive index when irradiated with ultraviolet light. this is,
It is considered that the Ge-related defects increase when the initial waveguide core film is subjected to a heat treatment in a non-oxidizing atmosphere.

As described above, according to the present invention, the number (density) of defects having absorption in the ultraviolet region is changed by controlling the atmosphere of the heat treatment and the degree (temperature and time) of the heat treatment. Also, it is possible to control the degree of the change in the refractive index induced by ultraviolet light irradiation within a desired range. Therefore, a light-induced refractive index change type waveguide suitable for forming an optical element such as a grating having desired characteristics by controlling the degree of change in the refractive index of the initial waveguide core film produced by the CVD method with respect to ultraviolet light irradiation. It becomes possible to produce a core film and a normal waveguide core film.

The heat treatment temperature in the oxidizing atmosphere and the non-oxidizing atmosphere may be higher than the deposition temperature (about 700 ° C. to about 800 ° C.) of the waveguide core film by the CVD method. When quartz glass is used as the material of the waveguide core film, it is preferable to perform the heat treatment at a temperature of about 1500 ° C. to about 1600 ° C. or less.

[0020]

Embodiments of the present invention will be described below.

(Embodiment 1) In this embodiment, a change in the photo-induced refractive index is controlled by a heat treatment (thermal annealing) in an oxidizing atmosphere.

As shown in FIG. 1, the waveguide core film of this embodiment is manufactured by performing an initial waveguide core film deposition process by a CVD method and a heat treatment (thermal annealing) process as a subsequent process. Hereinafter, a description will be given together with a comparative example.

Ge-doped SiO ₂ as a waveguide core film
A core film was deposited on a silica substrate by the CVD method and the FHD method for comparison (see FIGS. 1 and 2).
The one deposited by the CVD method is referred to as a waveguide core film I (Example; see FIG. 1), and the one deposited by the FHD method is referred to as a waveguide core film II (comparative example; see FIG. 2). Both of the waveguide core films I and II have a Ge concentration of 3.5.
It was deposited so as to have a thickness of 7 μm by mol%. I and II are the waveguide core film deposition methods (CVD method and FH method).
D) respectively, and the initial waveguide core films Ias and IIas
The waveguide core films obtained by subjecting the (as-grown waveguide core film) to thermal annealing for x hours are referred to as waveguide core films I _xh and II _xh .

As the above-mentioned CVD method, specifically, LP
-CVD method (Low-pressure Plasma Chemical Vapor Depo
sition method; see, for example, JP-A-7-49429). This LP-CVD method belongs to a low-pressure plasma CVD method for generating high-frequency plasma at a low pressure. Specifically, in the LP-CVD method, the inside of a reaction vessel in which a heater is built in and an induction coil for generating plasma on the outer surface is disposed is brought into a predetermined reduced pressure state by a vacuum pump, and 800 ° C. higher than 700 ° C. the temperature conditions not exceeding supplies a predetermined flow rate of the raw material gas _{(SiCl 4, GeCl 4, O} 2 , etc.) while generating a high frequency plasma in the reaction vessel by applying a predetermined high-frequency voltage to the induction coil Thus, the waveguide core film I is deposited on the substrate in the reaction vessel.

Thereafter, a thermal annealing step was performed on each of the initial waveguide core films Ias and IIas obtained by the CVD method. In the thermal annealing step, the thermal annealing apparatus 100 shown in FIG. 3 was used and heated at 800 ° C. for a predetermined time by a heater under an oxygen atmosphere of 1 atm (atmospheric pressure). Preferably, the oxygen partial pressure is at least about 0.1 atm or more.

FIG. 3 shows an example of an apparatus used for thermal annealing according to the present embodiment. The thermal annealing apparatus 100 of FIG.
A heating unit 20 and an atmosphere control unit 40 are provided. The heating section 20 includes an electric furnace 22 and a combustion tube 24 arranged in the electric furnace 22. The sample (initial waveguide core films Ias and IIas) 28 is placed in the combustion tube 24 while being housed in the combustion boat 26. The heat released from the electric furnace 22 is supplied to a sample 28 disposed in the combustion tube 24.
If necessary, a circuit (not shown) for detecting the temperature of the sample 28 and controlling the electric furnace 22 may be provided. Combustion tube 24
Is provided to control the temperature of the sample 28 and the atmosphere around the sample 28 sufficiently and efficiently. Combustion tube 2
4 and the combustion boat 26 are formed using a known material having desired heat resistance.

The atmosphere control section 40 includes a cylinder 42 as a gas source, a pressure regulator 44 and a flow regulator 46. The gas stored in the cylinder 42 is
The pressure and the flow rate are adjusted by the pressure regulator 44 and the flow rate regulator 46, respectively, and are supplied into the combustion pipe 24. In the case where the thermal annealing in the oxygen atmosphere according to the present embodiment is performed in the air, the atmosphere control unit 40 can be omitted.

Although FIG. 3 illustrates an apparatus for supplying one type of gas, a configuration using a plurality of types of gases may be employed. Further, the atmosphere control unit 40
In order to maintain the inside of the heating unit 20 in a reduced pressure atmosphere, a configuration including a chamber and a gas exhaust system may be adopted. In addition, a known heating device can be widely used in place of the electric furnace 22, and for example, an infrared heating furnace or an infrared laser may be used.

Each initial waveguide core film Ias and IIas has K
A predetermined number of shots were irradiated with ultraviolet laser light by an rF excimer laser (LPX105i manufactured by Lambda Physik, photon energy: 5.0 eV, energy density per pulse: 80 mJ / cm ² ).

For each of the above-mentioned waveguide core films I and II (initial and ultraviolet laser light irradiation), measurement of absorption spectrum and electron spin resonance (Electron Spin Resonance; ESR) using JES-PX1060 manufactured by JEOL.
The glass structure change induced by the irradiation of the ultraviolet laser light was observed by measuring the defect state by the method. The influence of the heat treatment on the glass structure of the waveguide core film was observed by measuring the absorption spectrum of each of the waveguide core films I and II (initial and after thermal annealing).

In addition, each of the above waveguide core films I and II
(Initial and after thermal annealing), using a scanning electron microscope (SEM; S2500CX manufactured by Hitachi, Ltd.) for each surface property before and after etching with an HF solution (hydrofluoric acid solution; about 10% aqueous solution). And observed.

The above measurements and the irradiation of ultraviolet laser light were all performed at room temperature.

(Absorption Spectra Before and After Thermal Annealing) The above-described initial waveguide core films Ias and IIas, and the waveguides obtained by subjecting each of the initial waveguide core films Ias and IIas to thermal annealing for 1 hour, 3 hours and 5 hours Core films I and II
About UV-3100PC manufactured by Shimadzu Corporation
Was used to measure the absorption spectrum.

Each of the above-mentioned initial waveguide core films I before thermal annealing
FIG. 4 shows the absorption spectra of as and IIas in the initial waveguide core films Ias and the waveguide core films I _1h , I _3h and I _{3 for} each elapsed time of thermal annealing for 1, 3 and 5 hours.
Each absorption spectrum for _5h is shown in FIG.

Referring to FIG. 4, in the initial waveguide core film Ias, the oxygen deficiency defect of Ge (Geoxygen-deficient center) was observed.
s; hereinafter referred to as “GODC”), while an absorption band at 5.1 eV appears, whereas the initial waveguide core film IIas
No such absorption band has appeared. Therefore, while the initial waveguide core film Ias is oxygen-deficient glass,
The initial waveguide core film IIas is not oxygen-deficient glass,
This initial waveguide core film IIas is considered to be a glass suitable for forming a normal waveguide which is more stable to ultraviolet light.

Referring to FIG. 5, the initial waveguide core film I
When thermal annealing is performed on as, it can be seen that the absorption band of 5.1 eV caused by the GODC decreases as the execution time of the thermal annealing increases. That is, the above 5.1e
Absorption peak of the absorption band of V becomes the low value towards the waveguide core layer I _1h after thermal annealing for one hour than the initial waveguide core layer Ias before thermal annealing, than the waveguide core layer I _1h Also, the waveguide core film _I3h after the thermal annealing for 3 hours has a lower value as the thermal annealing time elapses. After the thermal annealing for 5 hours, the absorption intensity of the 5.1 eV absorption band of the waveguide core film I _5h is reduced to about one fifth of that of the initial waveguide core film Ias.
Therefore, by subjecting the initial waveguide core film Ias to thermal annealing for more than 5 hours, the absorption peak value in the 5.1 eV absorption band is reduced to almost the same level as the absorption spectrum of the initial waveguide core film IIas. Conceivable. That is, a light-induced refractive index change type waveguide core film (initial waveguide core film Ias) in which an ultraviolet light-induced refractive index change is caused by the 5.1 eV absorption band is subjected to thermal annealing for 5 hours or more. This makes it possible to change to a normal waveguide core film (I _5h ) in which the ultraviolet light-induced refractive index change hardly occurs. On the other hand, in the case of the waveguide core film II, even if the above thermal annealing was performed, there was no significant change in the absorption spectrum before and after the thermal annealing.

In each of the absorption spectra in FIGS. 4 and 5, the horizontal axis represents photon energy (Photon Energy), and the vertical axis represents absorbance (Absorbance; -log ₁₀ (I / I ₀ )). Where I ₀ and I are the light intensities before and after passing through the sample, respectively, and represent the absorption characteristics determined by the absorbance with respect to the photon energy (see FIGS. 10, 13, 14, and 14 to be described later). 16)). (Properties before and after thermal annealing) Each of the above initial waveguide core films Ias
And IIas, and these initial waveguide core films Ias and IIas
Waveguide core film I after thermal annealing for 5 hours
_{For 5h} and II _5h , a comparative observation of the surface properties was performed.

Each of the initial waveguide core films Ias and IIas before the thermal annealing had a very smooth surface regardless of the difference in the deposition method. Then, the surfaces of both of these initial waveguide core films Ias and IIas were etched with the HF solution. As a result, the initial waveguide core film Ias
FIG. 6 shows the surface property S after the etching process.
While the microstructure having fine irregularities as shown in the EM photograph was obtained, the initial waveguide core film IIas was replaced by the initial waveguide core film IIas shown in FIG. The surface was smoother than Ias.

It is well known that SiO ₂ can be dissolved by HF but GeO ₂ cannot be dissolved by HF. Therefore, the degree of etching by HF differs depending on the difference in Ge amount. Therefore, the unevenness of the initial waveguide core film I as described above is such that the Ge distribution is not uniform,
In other words, this is considered to be due to the non-uniformity of the GeO ₂ distribution caused by the non-uniformity of the Ge distribution, such as the presence of a Ge-rich region and a poor region. Therefore, it is considered that even if the initial waveguide core film Ias was subjected to the etching treatment with the HF solution, the surface after the etching did not become smooth. In addition, G of the initial waveguide core film Ias
It is considered that a large amount of GODC is concentrated in the e-rich region. This means that the above-mentioned absorption spectrum measurement results (the presence of an absorption band at 5.1 eV due to GODC)
Is consistent with

On the other hand, in the initial waveguide core film IIas, G
It is considered that the distribution of e is almost uniform. And
The fact that the surface of the initial waveguide core film IIas after the HF etching treatment is in a smooth state as shown in FIG. 7 indicates that the Ge distribution is essentially uniform. This means that 5.1 eV in the absorption spectrum
This corresponds to the absence of the absorption band at.

Next, each of the initial waveguide core films Ias and
IIas (one not subjected to the etching treatment with the HF solution) is subjected to a thermal annealing for 5 hours, and Has described above.
The etching process was performed with the F solution. The surface of the waveguide core film _I5h after the thermal annealing and before the etching treatment had finer irregularities than the irregularities shown in FIG. As described above, the Ge distribution in the waveguide core film I is non-uniform. It is considered that a large stress is applied between the portion where the Ge concentration is high and the portion where the Ge concentration is low in the waveguide core film I. From this, it is considered that the unevenness on the surface after the heat treatment was raised due to the relaxation of such stress by heat. It is also conceivable that the surface may be raised due to the difference in thermal expansion coefficient between SiO ₂ and GeO ₂ . Waveguide core film II _5h after thermal annealing and before etching
Had a very smooth surface profile similar to that before thermal annealing. On the other hand, the waveguide core film I after thermal annealing
_{When the} above-mentioned etching treatment was performed on _5h and II _5h , in the waveguide core film I _5h , FIG. 8 shows an SEM photograph of the surface properties after the etching treatment. The waveguide core film II _5h is etched more uniformly than the case of the waveguide core film Ias, while the SEM photograph similar to FIG. 8 shows the waveguide core film II _5h as shown in FIG. There was no significant change compared to the waveguide core membrane IIas.

The change from the initial waveguide core layer Ias to the waveguide core layer I _5h is, Ge-rich regions by thermal annealing in the initial waveguide core layer Ias (Ge-doped layer) is reduced Ge (GeO ₂ This is considered to be due to the more uniform distribution, and this uniform Ge distribution is considered to be G from the viewpoint of glass quality as a normal waveguide core film.
It is considered that the glass quality of the e-doped layer was improved.

That is, in the initial waveguide core film Ias, the intensity of the absorption band at 5.1 eV is reduced by thermal annealing in an oxidizing atmosphere (in an oxygen atmosphere), and FIG.
The each phenomenon of the initial waveguide core layer waveguide core after thermal annealing the Ias film I _5h is uniformly etched by dissolution with HF as SEM photographs, the waveguide after thermal annealing the core layer I _5h Is caused by the homogenization of the Ge distribution in. Thereby, the quality of the Ge-doped layer is improved as described above. (Change due to UV Laser Light Irradiation) FIG. 10 shows that the above initial waveguide core film Ias was irradiated with the UV laser light by the KrF excimer laser for 3000 times.
An absorption spectrum before shot irradiation (see Ibi in FIG. 10) and an absorption spectrum after irradiation (see Iai in FIG. 10) are shown. In addition, FIG. 11 shows the increase in absorbance obtained by subtracting the absorption spectrum Ibi before irradiation from the absorption spectrum Iai after irradiation described above, and the amount of induced absorption (ΔAbsorban) induced by ultraviolet laser beam irradiation.
ce). A waveguide core film having a larger change in absorbance due to irradiation with ultraviolet laser light has a larger change in light-induced refractive index, and is suitable for forming an optical element such as a grating.

The induced absorption spectrum in FIG.
Induction of a Ge electron center (Ge electron capture center; hereinafter referred to as "GEC") having an absorption band at each peak position at 5 eV and 5.8 eV, and induction of a GeE 'center having an absorption band at the peak position at 6.4 eV. It is considered to be due to The downward peak at 5.1 eV is considered to be due to a decrease in GODC.

On the other hand, when the initial waveguide core film IIas was irradiated with an ultraviolet laser beam using a KrF excimer laser in the same manner as described above, no change in the absorbance related to Ge was induced as compared with before the irradiation. However, a slight change in absorbance was induced in the silica substrate.

FIG. 12 shows the initial waveguide core film Ias described above.
The ESR signals measured by the electron spin resonance method (X band) are shown for the case where the number of shots of ultraviolet laser light irradiation on the initial waveguide core film Ias is sequentially increased. FIG. 12 shows, in order from the top, one before irradiation with ultraviolet laser light (E-1), one after irradiation with 10 shots of ultraviolet laser light (E-2), and one after irradiation with 100 shots (E -3), those irradiated with 1000 shots (E-4), and those irradiated with 3000 shots (E
-5), and a Ge-doped layer removed by dissolving with HF from the 3000-shot irradiated one (a waveguide core film removed to a silica substrate only).
Each ESR signal of (E-6) is shown side by side in the same drawing.

Referring to the ESR signals shown in FIG. 12, the SiE'center (E prime center of Si) shows before and after the irradiation of the ultraviolet laser beam (E-1 to E-5), and
Since the Ge-doped layer was removed after the irradiation of the 00 shot ultraviolet laser beam (E-6), it was observed regardless of whether the Ge-doped layer was removed (E-6). Therefore, the SiE'center shown in FIG. 12 was present on the silica substrate. I understand.

On the other hand, in the initial waveguide core film Ias,
It can be seen that GEC and GeE'center, which are paramagnetic defects, are induced by the irradiation of the ultraviolet laser light, and the amount of the induction increases with an increase in the number of irradiation shots.
reference). Such induction of paramagnetic defects by irradiation with ultraviolet laser light is consistent with the above measurement results of the absorption spectrum (absorption induction by irradiation with ultraviolet laser light). On the other hand, in the initial waveguide core film IIas, the above paramagnetic defect was not detected before and after the irradiation of the ultraviolet laser light.

That is, since GODC is sensitive to ultraviolet light and greatly contributes to the change of the photo-induced refractive index,
In the initial waveguide core film Ias where GODC exists, K
GEC and GeE 'by irradiation with rF excimer laser
While two types of paramagnetic defects, center, are induced, the above initial waveguide core film without GODC exists.
In IIas, the above paramagnetic defect is not induced.

As described above, in the initial waveguide core film Ias deposited by the CVD method, the Ge distribution was non-uniform and GODC was observed. It has been found that thermal annealing in an oxygen atmosphere reduces GODC and improves the quality of the Ge-doped layer. In addition, it has been found that irradiation of the initial waveguide core film Ias with ultraviolet laser light induces paramagnetic defects called GEC and GeE'center. As a result, it is understood that the initial waveguide core film Ias is suitable for manufacturing an optical element (for example, an optical communication device such as a grating). Therefore, while the initial waveguide core film Ias can be applied as a photoinduced refractive index change type waveguide core film, it is not usually used as a photoinduced refractive index change type waveguide core film by performing thermal annealing. Can be changed to one suitable for use as a waveguide core film. In other words, the post-processing (thermal annealing) of the ultraviolet light-induced refractive index change characteristics of the deposited waveguide core film
Can be changed by

In the above-described example, the present embodiment has been described by taking an oxygen gas atmosphere (1 atm) as an example of the oxidizing atmosphere. However, the oxidizing atmosphere in the thermal annealing step of the present embodiment is not limited to the above example. The partial pressure is preferably about 0.1 atm or more, more preferably about 0.5 atm or more (however, substantially no reducing hydrogen gas is contained). Although there is no particular upper limit for the oxygen partial pressure and the total pressure of the atmosphere, it is preferably at most atmospheric pressure (1 atm) for simplicity.

The heat treatment temperature in an oxidizing atmosphere is set at the deposition temperature of the waveguide core film by the CVD method (about 700 ° C. to 800 ° C.).
C.). The effect of this heat treatment becomes more remarkable as the temperature increases, and is considered to be caused by an Arrhenius-type reaction (thermal oxidation). Therefore, the upper limit of the heat treatment temperature may be appropriately determined depending on the heat resistance of the waveguide core film material. When using quartz glass as the waveguide core film material, it is preferable to perform the heat treatment at a temperature of about 1500 ° C. to about 1600 ° C. or less. The heat treatment time may be shorter as the heat treatment temperature is higher, and each atmosphere and the heat treatment temperature can be easily optimized.

When the initial waveguide core film is deposited by a CVD method in an oxygen-deficient atmosphere (for example, an oxygen partial pressure of less than about 0.1 atm), an initial waveguide core film containing many oxygen-deficient defects can be obtained. . The initial waveguide core film thus obtained is irradiated with UV light to form the GeE'cent
Since er increases, it has a large photo-induced refractive index change and can be suitably used for writing an optical element (grating or the like). By subjecting this initial waveguide core film to a heat treatment in the above-described oxidizing atmosphere as a post-treatment, a waveguide core film suitable for use as a normal waveguide core film having a small refractive index change due to ultraviolet light irradiation is obtained. can get.

As a method for forming an optical element on the waveguide core film of the present embodiment, for example, a fourth harmonic (266 nm) light of a YAG laser is applied to the waveguide core film by a phase mask method. Can be used. 4th harmonic of YAG laser (266n
m) Light has higher coherence than gas lasers,
A grating can be formed with high accuracy.

On the other hand, in the initial waveguide core film IIas deposited by the FHD method, no paramagnetic defect was induced even when irradiated with ultraviolet laser light. It is considered that the reason is that Ge is almost uniformly distributed, and that GODC is hardly present quantitatively in the waveguide core film. Therefore, it is considered that the initial waveguide core film IIas is suitable for being applied to the above-described ordinary waveguide core film used in a severe radiation field (eg, gamma ray) environment.

(Embodiment 2) In this embodiment, the change in the photo-induced refractive index is controlled by thermal annealing in a non-oxidizing atmosphere.

In the same manner as in the first embodiment, a Ge-doped SiO ₂ core film as a waveguide core film was deposited on a silica substrate by a CVD method. A Ge-doped SiO ₂ core film deposited by the CVD method is used as a waveguide core film III (Example).
And For comparison, Ge-doped S deposited on a silica substrate by the FHD method in the same manner as in Embodiment 1 was used.
The iO ₂ core film is referred to as a waveguide core film IV (comparative example). These waveguide core films III and IV were both deposited to a thickness of about 7 μm with the addition concentration of Ge being 3.5 mol%. That is, the initial waveguide core films IIIas and IVas
Are essentially the same as the initial waveguide core films Ias and IIas of the first embodiment, respectively.

Thereafter, the thermal annealing apparatus 100 shown in FIG. 3 is applied to each of the initial waveguide core films IIIas and IVas.
Was used to perform a thermal annealing step. In the method of manufacturing the waveguide core film of the present embodiment, the substrate was heated at about 1000 ° C. for a predetermined time in a non-oxidizing atmosphere. Here, a nitrogen gas atmosphere and a helium gas atmosphere (both 1 atm (atmospheric pressure)) were adopted as the non-oxidizing atmosphere. Specifically, the flow rates of the nitrogen gas and the helium gas were 100 ml / min (at 20 ° C.).

Further, each of the initial waveguide core films IIIas and IVa
s and the waveguide core films III _xh , IV _{xh obtained by} subjecting each of the initial waveguide core films IIIas and IVas to the above-mentioned thermal annealing for x hours, measuring the absorption spectrum and etching with the HF solution as in the first embodiment. SEM observation of each surface property before and after the treatment was performed.

(Absorption Spectra Before and After Thermal Annealing) Each of the initial waveguide core films IIIas and IVas and each of the waveguide core films III _xh and IV thermally annealed in a non-oxidizing atmosphere.
_{For xh} , the absorption spectrum was measured. The obtained absorption spectra are shown in FIGS.

FIG. 13 shows the initial waveguide core film IIIas and thermal annealing at about 1000 ° C. for 1 hour in a nitrogen gas atmosphere.
Waveguide core films III _1h , III _3h , performed for 3 hours and 5 hours,
And III _5h show absorption spectra. FIG. 14 shows an initial waveguide core film IIIas and about 10% in a helium gas atmosphere.
Each of the waveguide core films III _1h , III _2h , and III were subjected to thermal annealing at 00 ° C. for 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours.
₃ shows absorption spectra of _3h , III _4h and III _5h . As will be described later, since substantially the same result was obtained in the nitrogen gas atmosphere and the helium gas atmosphere, the names of the samples are not distinguished by gas type for simplicity.

As is clear from FIGS. 13 and 14,
Under a nitrogen gas atmosphere (FIG. 13), a spectrum change substantially the same as that obtained under a helium gas atmosphere (FIG. 14) was obtained. G of the initial waveguide core film IIIas
e due to oxygen deficiency defect (GODC)
It can be seen that the absorption band increases as the execution time of the thermal annealing increases. That is, the absorption peak value of the above 5.1 eV absorption band is determined by the initial waveguide core film before thermal annealing.
Waveguide core film III _1h after thermal annealing for 1 hour than IIIas
Is higher than that of the waveguide core film III _1h.
The waveguide core film III _3h after the time thermal annealing has a higher value. In the waveguide core film III _5h after the thermal annealing for 5 hours, the absorption intensity of the 5.1 eV absorption band is changed to the initial waveguide core film II.
It is about three times as large as Ias.

FIG. 15 shows waveguide core films III _1h , III
_FIG . 11 shows a difference spectrum of the absorption spectrum of _2h , III _3h , III _4h and III _5h with respect to the absorption spectrum of the initial waveguide core film IIIas. As is clear from FIG. 15, the absorption intensity at 5.8 eV decreases as the absorption intensity in the 5.1 eV absorption band increases with the increase in the annealing time. As described above, SiE'center exists in the substrate of the waveguide core film Ias. Since the waveguide core film IIIas is substantially the same as the waveguide core film Ias, SiE'center also exists in the substrate of the waveguide core film IIIas. This SiE'ce
nter has an absorption band with a peak value of 5.8 eV.
The downward peak at 5.8 eV in FIG. 15 is considered to be due to the decrease in SiE'center due to the heat treatment.

As can be seen from FIG. 16, in the case of the initial waveguide core film IVas deposited by the FHD method, similarly to the thermal annealing under the oxidizing atmosphere shown in the first embodiment, the thermal annealing under the non-oxidizing atmosphere is performed. Even after annealing, no substantial change in the absorption spectrum was observed before and after the thermal annealing.
This shows that the initial waveguide core film IVas deposited by the FHD method is a stable film regardless of the thermal annealing atmosphere (oxidizing atmosphere or non-oxidizing atmosphere).

[0065] and (thermal annealing before and after properties) each initial waveguide core layer of the IIIas and IVAS, each waveguide core layer was performed 5 hours thermal annealing in an atmosphere and under a helium gas atmosphere of nitrogen gas III _5h and IV _5h , Comparative observation of the respective surface properties was performed.

Each initial waveguide core film IIIas before thermal annealing
And IVas were essentially the same as the initial waveguide core films Ias and IIas of Embodiment 1, and both surfaces before etching were very smooth surfaces. In contrast, CVD
As shown in FIG. 6, fine irregularities were observed on the surface after etching the initial waveguide core film IIIas deposited by the method. The etched surface of the initial waveguide core film IVas deposited by the FHD method is smoother than the etched surface of the initial waveguide core film IIIa deposited by the CVD method, as shown in the SEM photograph in FIG. Surface.

After the above thermal annealing in the non-oxidizing atmosphere,
Core film before etching_5hAnd IV
_5hAre after thermal annealing in an oxidizing atmosphere, respectively.
Each waveguide core film I before etching processing_5hAnd II_5hSame as
Had the same surface shape. On the other hand, thermal annealing was performed
Waveguide core film III_5hWhen the above etching process is applied to
Waveguide core film after thermal annealing III_5hBefore thermal annealing
Compared to the initial waveguide core film III (Fig. 6), the
It was touched. Waveguide core film after thermal annealing IV _5hOn
The surface properties of the film that has been subjected to the etching
The initial waveguide core film IVas before etching was etched.
There was no significant difference compared to the surface properties of the film. Sand
Waveguide core film by thermal annealing in non-oxidizing atmosphere
The effect on the properties (uniformity) of the film depends on the film deposited by CVD.
Also for films deposited by the FHD method
Is the same as the thermal annealing in the oxidizing atmosphere described above.
Met. That is, waveguides deposited by the CVD method.
The uniformity of the path core film depends on the atmosphere (oxidizing atmosphere or non-oxidizing
Regardless of improvement by thermal annealing regardless of atmosphere)
Of waveguide core film deposited by FHD method
Is not affected by thermal annealing, and
It can be seen that the uniformity is high. Deposited by CVD
For the waveguide core film, regardless of the atmosphere,
Also, the Ge distribution became uniform. Therefore, this phenomenon
The heat generated in the waveguide core film by the processing
It is thought that it was.

As described above, the initial waveguide core film (Ge-doped quartz glass core film) deposited by the CVD method is thermally annealed in a non-oxidizing atmosphere (nitrogen gas or helium gas atmosphere). 5.1 eV
Since the intensity of the absorption band can be increased and the film quality can be improved, a light-induced refractive index change type waveguide core film having excellent characteristics can be manufactured. In addition, since the initial waveguide core film can be deposited in the same process as a normal waveguide core film, a light-induced refractive index change type waveguide core film is manufactured by a simpler manufacturing method than before. can do.

In the above-described example, the present embodiment has been described by taking the nitrogen gas atmosphere and the helium gas atmosphere as examples of the non-oxidizing atmosphere. However, the non-oxidizing atmosphere in the thermal annealing step of the present embodiment is the inert gas ( It is not limited to an atmosphere including a rare gas represented by helium and a nitrogen gas) and is a reduced pressure atmosphere (oxygen partial pressure less than about 0.1 atm)
Alternatively, a reducing atmosphere containing hydrogen gas may be used.

The heat treatment temperature in a non-oxidizing atmosphere is as follows:
The deposition temperature of the waveguide core film by the CVD method (about 700 ° C.
800 ° C.). The effect of this heat treatment becomes more remarkable as the temperature increases, and is considered to be caused by an Arrhenius-type reaction. Therefore, the upper limit of the heat treatment temperature may be appropriately determined depending on the heat resistance of the waveguide core film material. When using quartz glass, about 1500
Preferably, the heat treatment is performed at a temperature of from about ℃ to about 1600 ℃. The heat treatment time may be shorter as the heat treatment temperature is higher, and each atmosphere and the heat treatment temperature can be easily optimized.

As described above, the initial waveguide core film (a quartz glass doped with a normal amount of Ge) formed as a normal waveguide core film is thermally annealed in an oxidizing atmosphere to change the photoinduced refractive index. Can be reduced, and the thermal induced annealing in a non-oxidizing atmosphere can increase the photoinduced refractive index change. Furthermore, the film quality (uniformity) is improved by thermal annealing regardless of the atmosphere, so that the optical transmission loss can be reduced. That is, by simply adding a heat treatment or changing the heat treatment conditions to the waveguide core film deposited by the same method as the conventional method, a normal waveguide core film having better characteristics than the conventional and a light-induced refractive index change type Both waveguide core films can be made. Therefore, a waveguide core film having excellent characteristics can be efficiently formed by a simple manufacturing method.

Further, when heat treatment is performed in an oxidizing atmosphere, a part of the initial waveguide core film (a region where the photoinduced refractive index change is to be increased) is masked so as not to be exposed to oxygen. The change in the photo-induced refractive index of the initial waveguide core film in the region where the light-emitting layer is located can be locally (selectively) increased. Alternatively, by locally performing heating in an oxidizing atmosphere or a non-oxidizing atmosphere, the photoinduced refractive index change can be locally reduced (in an oxidizing atmosphere) or increased (in a non-oxidizing atmosphere). Of course, the region exposed to the atmosphere may be defined using a mask, and the region may be heated locally. Specifically, for example, in order to selectively form a region where the photoinduced refractive index change is large, a part of the initial core film may be masked and the masked region may be locally heated. Conversely, a region other than a region where the photoinduced refractive index change is to be increased may be selectively heated in an oxidizing atmosphere. When selectively heating a region where the photoinduced refractive index change is to be increased in a non-oxidizing atmosphere, formation of a mask in a region where the photoinduced refractive index change is to be increased may be omitted. In order to form a waveguide core film with a large photoinduced refractive index change by combining thermal annealing in an oxidizing atmosphere with thermal annealing in a non-oxidizing atmosphere, thermal annealing in a non-oxidizing atmosphere must be performed first. After that, it is preferable to perform thermal annealing in an oxidizing atmosphere.

As a mask, for example, silicon nitride (SiN _x ) or silicon oxide (SiO _x ) can be used. Local heating can be performed using, for example, an infrared laser.

[0074]

According to the present invention, by controlling the atmosphere and the degree (temperature and time) of the heat treatment as the post-treatment with respect to the initial waveguide core film deposited by the CVD method, the ultraviolet region can be controlled. Thus, the number (density) of defects having absorption can be changed, and as a result, it is possible to control the degree of change in the photo-induced refractive index with respect to ultraviolet light within a desired range. Therefore, by controlling the degree of change in the refractive index of the initial waveguide core film deposited by the CVD method with respect to ultraviolet light irradiation,
It becomes possible to produce a photoinduced refractive index change type waveguide core film having desired characteristics and a normal waveguide core film.

The optically induced refractive index changing waveguide core film according to the present invention can be used for forming an optical element for optical communication, for example, a grating having a short cycle (pitch of 1 micron or less) or a long cycle (about 100 μm to about 500 μm). It is suitably used for forming a grating having a pitch of (micron).

[Brief description of the drawings]

FIG. 1 is a block diagram showing each step of an embodiment of the present invention.

FIG. 2 is an explanatory block diagram showing each step of a comparative example.

FIG. 3 is a schematic diagram illustrating an example of a thermal annealing apparatus used in an embodiment of the present invention.

FIG. 4 is an absorption spectrum of initial waveguide core films Ias and IIas.

FIG. 5 is an absorption spectrum of the initial waveguide core film Ias after thermal annealing in an oxidizing atmosphere.

FIG. 6 shows SE after HF treatment of an initial waveguide core film Ias.
It is the figure which digitized M photograph.

FIG. 7 shows SE after HF treatment of initial waveguide core film IIas.
It is the figure which digitized M photograph.

FIG. 8 shows an initial waveguide core film Ias in an oxidizing atmosphere for 5
It is the figure which digitized the SEM photograph after time thermal annealing and HF processing.

FIG. 9 shows the relationship between the initial waveguide core film IIas under an oxidizing atmosphere;
It is the figure which digitized the SEM photograph after time thermal annealing and HF processing.

FIG. 10 is an absorption spectrum of a waveguide core film I before and after irradiation with an ultraviolet laser beam.

FIG. 11 is an induced absorption spectrum induced by irradiation with ultraviolet laser light.

FIG. 12 is a graph showing E of the waveguide core film I by irradiating an ultraviolet laser beam.
It is a figure showing change of SR signal.

FIG. 13 is an absorption spectrum of the initial waveguide core film IIIas after thermal annealing in a non-oxidizing atmosphere (nitrogen gas).

FIG. 14 is an absorption spectrum after thermal annealing of an initial waveguide core film IIIas in a non-oxidizing atmosphere (helium gas).

FIG. 15 is a difference spectrum between the absorption spectrum after thermal annealing and the absorption spectrum before thermal annealing in a non-oxidizing atmosphere (helium gas) for the initial waveguide core film IIIas.

FIG. 16 is an absorption spectrum of the initial waveguide core film IVas after thermal annealing in a non-oxidizing atmosphere (helium gas).

[Explanation of symbols]

 Reference Signs List 20 heating unit 22 electric furnace 24 combustion tube 26 combustion boat 28 sample 40 atmosphere control unit 42 cylinder 44 pressure regulator 46 flow regulator 48 piping 100 thermal annealing device

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kazuo Imamura 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Electric Cable Industry Co., Ltd. Itami Works F-term (reference) 2H047 PA05 PA11 QA04 RA00 TA00 4G014 AH15 4G059 EA01 EB01

Claims (9)

[Claims] 1. A waveguide core film comprising a Ge-doped quartz glass core film, wherein the Ge-doped quartz glass core film deposited on a substrate by a CVD method is at least in an oxidizing atmosphere. A waveguide core film, which is heat-treated at a higher temperature than at the time of deposition. 2. The waveguide core film according to claim 1, wherein the deposition of the quartz glass core film by the CVD method is performed in an oxygen-deficient atmosphere. 3. A waveguide core film comprising a Ge-doped quartz glass core film, wherein the Ge-doped quartz glass core film deposited on a substrate by a CVD method is treated in a non-oxidizing atmosphere. A waveguide core film which is heat-treated at least at a temperature higher than the temperature at the time of deposition. 4. The waveguide core film according to claim 3, wherein a grating is formed in the waveguide core film. 5. A waveguide core film forming method for forming a Ge-containing quartz glass core film, comprising: depositing a quartz glass core film on a substrate while adding Ge by a CVD method; A step of subjecting the quartz-based glass core film to a heat treatment at a temperature higher than at least the deposition step in an oxidizing atmosphere after the step. 6. The method according to claim 5, wherein the deposition step is performed in an oxygen-deficient atmosphere. 7. A waveguide core film forming method for forming a Ge-based quartz glass core film, comprising: depositing a quartz-based glass core film on a substrate while adding Ge by a CVD method; A step of subjecting the quartz-based glass core film to a heat treatment in a non-oxidizing atmosphere at a temperature higher than at least the deposition step, after the depositing step. 8. The method according to claim 7, wherein the non-oxidizing atmosphere in the heat treatment step is an inert gas atmosphere. 9. The method according to claim 7, further comprising a step of irradiating at least a part of the quartz glass core film subjected to the heat treatment in the non-oxidizing atmosphere with ultraviolet light to form a grating. Of manufacturing a waveguide core film.