JP2001133649A - Method for manufacturing optical waveguide grating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently manufacture gratings of fine periods by easily forming fine regions varying in refractive indices in flush the optical waveguides of an ion-exchange type. SOLUTION: Changes in the refractive indices of the fine periods are imparted into the optical waveguides of the flush type by devising production processes, the relationship between a glass substrate and doping ion species, the doping ion species, etc., and executing ion exchanges, using a metallic mask for forming striped gratings. Typical method has an ion exchange stage for executing the thermoion exchange by providing the surface of the glass substrate 10 with the metallic mask 12 for forming the optical waveguide patterns, a stage for removing the metallic mask, an ion-exchange stage for forming the flush type optical waveguides 16 by executing the electric field impressed ion exchange for embedding the ion-exchanged refractive index increase portions 14, an ion exchange stage for forming the fine regions 20 by disposing the metallic mask 18 for forming the gratings and executing the ion exchange with ions of a high concentration, while imparting electric fields thereto and a stage for removing the metallic mask.

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 an optical waveguide grating which forms a fine-period refractive index change in the light propagation direction on an optical waveguide embedded in a glass substrate by an ion exchange method using a striped metal mask. It is about the method. This technique is useful for manufacturing an ion-exchange optical waveguide grating used as a wavelength division multiplexing / demultiplexing element for multiplexing or demultiplexing an optical signal of a predetermined wavelength.

[0002]

2. Description of the Related Art In a planar waveguide type optical circuit, there are an ion exchange method and a flame deposition method as typical methods for forming the optical waveguide. The ion exchange method uses a multi-component glass as a substrate and immerses it in a molten salt to form an optical waveguide by thermal ion exchange or electric field applied ion exchange, and is a low-temperature process (about 200 to 500 ° C.). This method has the advantage of being easy and inexpensive to manufacture. On the other hand, in the flame deposition method, an optical waveguide is formed by depositing a silica-based glass on a Si substrate.
About 300 ° C.). This method is exposed to high temperatures during the manufacturing process, so that internal stress and the like act anisotropically, the polarization dependent loss that is important in optical communication is large, the manufacturing method is complicated, and the cost increases.

Meanwhile, a grating is an extremely important technique for forming an optical circuit. This grating has a fine periodic structure formed in an optical waveguide, and is applied to various optical devices such as a wavelength filter, a reflector, and a mode converter.

[0004] In the case of a fiber grating, it is formed by utilizing the fact that the refractive index of a glass material constituting an optical fiber changes by irradiation with ultraviolet light. As a specific method, a transmission diffraction grating (phase mask) having irregularities formed on the surface of quartz glass is installed, and interference fringes of ultraviolet light are reduced by +1.
There is a method of forming by interference between the first and second order transmitted diffraction light. This method is excellent in reproducibility because the pitch of the interference fringes is の of the grating period of the phase mask. As another method, the ultraviolet light is split into two equal intensity light beams by a half mirror, and the optical paths of the two light beams are changed by a total reflection mirror arranged in parallel with each other, and cross each other on an optical fiber. Irradiation method. In this method, two light beams interfere with each other on an optical fiber, and a period Λ = λ /
A light intensity distribution of interference fringes of 2 sin θ is formed. Where λ
Is the wavelength of the ultraviolet light, and θ is the incident angle of the ultraviolet light incident on the optical fiber.

In general, in Ge-doped optical fibers, optical damage is caused by the irradiation of ultraviolet light, and the refractive index of the irradiated portion increases. Accordingly, a periodic change in the refractive index corresponding to the light intensity distribution of the interference fringes occurs in the core of the optical fiber on which the interference fringes of the ultraviolet light are formed. That is, a change in the refractive index having a constant width and period occurs in a portion irradiated with ultraviolet light, and a constant refractive index is maintained in other portions. With such a refractive index distribution, an optical filter that selectively reflects only the wavelength component of the wavelength 2n２ and transmits light of other wavelength components with low loss is formed. Here, n is the average refractive index of the optical fiber core.

[0006] In the case of a planar waveguide type optical circuit, in the case of an optical waveguide formed by the flame deposition method, the core is doped with Ge, so that the grating is formed in the optical waveguide by irradiating ultraviolet light as in the case of the fiber grating. Can be formed.

[0007]

An optical waveguide formed by the flame deposition method has a large polarization dependence, and this type of planar waveguide optical circuit requires a complicated manufacturing method and is expensive. Therefore, the grating also has polarization dependence and is expensive. On the other hand, waveguide-type optical circuits using the ion exchange method are easy to manufacture and inexpensive. However, the diffusion coefficient and the concentration dependence of the diffusion coefficient differ depending on the glass material and the doped ion species. The production is said to be difficult due to the spontaneous diffusion of ions due to heat, which cannot be controlled even if a concentration modulation of a submicron cycle is caused.

Further, there has been reported an attempt to produce a waveguide on a glass surface by an ion exchange method to cause ion concentration modulation. However, in the case of a surface optical waveguide, the waveguide shape has anisotropy. The polarization dependence is large and the loss is large. On the other hand, the buried type is effective in reducing the loss. However, since the optical waveguide is buried to about 10 μm, the grating must be diffused while maintaining the density modulation in the lateral direction to the depth. for that reason,
An effective method for accurately producing a grating having a small period in such an embedded optical waveguide has not been developed yet.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of efficiently forming a grating having a desired fine period by making it possible to easily form fine regions having different refractive indices in an ion-exchange type embedded optical waveguide. It is.

[0010]

According to the present invention, an ion-exchange type optical waveguide is embedded in a glass substrate, and an optical waveguide grating whose refractive index changes at a predetermined fine period in the light propagation direction is formed in the optical waveguide. How to In the present invention, ion exchange is performed using a metal mask for forming a striped grating by devising a manufacturing process, a relationship between a glass substrate and a doped ion species, or a doped ion species, so that a fine optical waveguide is formed in an embedded optical waveguide. This is a method for manufacturing an optical waveguide grating that forms a periodic refractive index change.
The stripe-shaped metal mask for forming a grating has a structure in which a large number (for example, tens of thousands) of linear openings are arranged in stripes at a period of, for example, 0.2 to 1.0 μm.

The first method includes a first ion exchange step of providing a metal mask for forming an optical waveguide pattern on the surface of a glass substrate to perform thermal ion exchange, a step of removing the metal mask for forming an optical waveguide pattern, A second ion exchange step of performing an electric field application ion exchange to embed the exchanged refractive index increasing portion in the glass substrate to form a buried optical waveguide, providing a stripe-shaped grating forming metal mask on the surface of the glass substrate, A third ion exchange step of periodically controlling the ion concentration distribution without distorting the shape of the optical waveguide by performing ion exchange with a higher concentration of the same kind of ions than during the first ion exchange while applying an electric field; Removing the metal mask for forming the grating.

In the second method, a combination of an ion and a glass having a strong ion concentration dependence of a mutual diffusion coefficient of doped ions in the glass is selected. Then, a first ion exchange step of providing a metal mask for forming an optical waveguide pattern on the surface of the glass substrate to perform thermal ion exchange, a step of removing the metal mask for forming the optical waveguide pattern, and a step of ion-exchanged increasing the refractive index are performed. A second ion exchange step of forming a buried type optical waveguide by performing an electric field application ion exchange to embed in the glass substrate, and providing a stripe-shaped grating forming metal mask on the surface of the glass substrate and starting from the first ion exchange. A third ion exchange step of performing thermal ion exchange with high-concentration ions of the same kind, a step of removing the metal mask for forming the grating, and an electric field application for embedding the ion-exchanged portion in the third ion exchange step to the optical waveguide portion. By performing the ion exchange, the fourth ion concentration controlling the ion concentration distribution periodically without breaking the shape of the optical waveguide. Exchange process, which comprises a.

In a third method, a metal mask for forming an optical waveguide pattern is provided on the surface of a glass substrate, and ion exchange is performed using ions whose ion exchange proceeds at a high temperature and does not proceed at a low temperature, and a buried optical waveguide is formed. Forming a
Providing a metal mask for forming a grating in the form of a stripe on the surface of the glass substrate, forming a fine region having a different refractive index in the optical waveguide by performing electric field application ion exchange using ions whose ion exchange proceeds at a low temperature. I have.

[0014]

FIG. 1 shows an example of a manufacturing process according to a first method. (1-a) An optical waveguide pattern forming metal mask 12 is provided on the surface of a glass substrate 10. (1-b) Thermionic exchange is performed through the opening of the metal mask 12 for forming an optical waveguide pattern to form a refractive index increasing portion 14 that becomes an optical waveguide. (1-c) The metal mask for forming the optical waveguide pattern is removed, and then an electric field application ion exchange is performed to embed the ion-exchanged refractive index increasing portion in the glass substrate to form a buried optical waveguide 16. (1-d) A stripe-shaped grating forming metal mask 18 having a linear opening in a direction crossing the optical waveguide is provided on the substrate surface immediately above the embedded optical waveguide 16 of the glass substrate 10, and an electric field is applied. The ion exchange is performed with a higher concentration of the same kind of ions than during the first ion exchange. Reference numeral 20 denotes a fine region subjected to ion exchange. (1-e) The grating-forming metal mask is removed. This makes it possible to control the ion concentration distribution periodically without changing the shape of the optical waveguide, thereby forming a fine periodic refractive index change.

The voltage applied in the step (1-d) is set so that ions can be diffused to a desired depth before the concentration distribution in the lateral direction of the grating portion is lost due to thermal diffusion. This method is effective whatever the relationship between the doped ion concentration and the diffusion coefficient.

FIG. 2 shows an example of a manufacturing process according to the second method. (2-a) An optical waveguide pattern forming metal mask 32 is provided on the surface of the glass substrate 30. (2-b) Thermionic exchange is performed through the opening of the metal mask 32 for forming an optical waveguide pattern to form a refractive index increasing portion 34 that becomes an optical waveguide. (2-c) The metal mask for forming the optical waveguide pattern is removed, and then an electric field application ion exchange is performed to embed the ion-exchanged refractive index increasing portion in the glass substrate, thereby forming a buried optical waveguide 36. The steps up to this step are the same as in the first method. (2-d) On the substrate surface immediately above the embedded optical waveguide 36 of the glass substrate 30, a stripe-shaped grating forming metal mask 38 having a linear opening in a direction crossing the optical waveguide is provided to perform first ion exchange. Thermal ion exchange with higher concentration of the same kind of ions than at the time. The ion exchanged fine region is indicated by reference numeral 39. (2-e) removing the metal mask for forming the grating;
Next, an electric field application ion exchange is performed in order to bury the fine region ion-exchanged in the ion exchange step (2-d) up to the optical waveguide portion. The embedded fine refractive index increasing region is indicated by reference numeral 40.

In this method, a combination of a glass and an ionic species whose interdiffusion coefficient of ions to be doped greatly depends on the concentration of the doped ions in the glass is selected.
Through the step (2-d), the optical waveguide grating can be manufactured by controlling the ion concentration distribution without disturbing the period of the minute pitch due to natural diffusion.

FIG. 3 shows an example of a manufacturing process according to the third method. (3-a) An optical waveguide pattern forming metal mask 52 is provided on the surface of the glass substrate 50. (3-b) Thermionic exchange is performed through the opening of the metal mask 52 for forming an optical waveguide pattern to form a refractive index increasing portion 54 that becomes an optical waveguide. (3-c) The metal mask for forming the optical waveguide pattern is removed, and then an electric field application ion exchange is performed to embed the ion-exchanged refractive index increasing portion in the glass substrate to form a buried optical waveguide 56. Up to this step, it is the same as the first method. (3-d) A stripe-shaped grating-forming metal mask 58 having a linear opening in a direction crossing the optical waveguide is provided on the substrate surface immediately above the embedded optical waveguide 56 of the glass substrate 50, and ion exchange is performed at a low temperature. Electric field application ion exchange is performed by using traveling ions, and fine regions 60 having different refractive indexes are used.
To form (3-e) The metal mask for forming the grating is removed.

In the third method, for example, Tl ions are used for forming an optical waveguide, and Ag ions are used for forming a grating. Tl ions have a small mutual diffusion coefficient in glass, and ion exchange does not proceed unless the temperature is relatively high, around 500 ° C. On the other hand, ion exchange of Ag ions proceeds at a temperature of about 300 ° C. or less. Therefore, a buried optical waveguide is prepared by Tl ion exchange at a processing temperature of about 500 ° C. in advance, and a stripe-shaped mask is provided immediately above the optical waveguide, and Ag ions are applied at a temperature of 300 ° C. or less by electric field application ion exchange. Then, the optical waveguide grating can be manufactured by ion exchange without breaking the shape of the already manufactured optical waveguide.

[0020]

EXAMPLE A soda-lime glass was used as a glass substrate, Ag ions were used as doped ion species, and a stripe-shaped metal mask for forming a grating (grating period: 0.5 μm) was used. As a result, a reflectance of about 60% was obtained, and a grating could be formed.

Two kinds of glasses (glass A and glass B) having different compositions were used as glass substrates, and AgN was used as a molten salt.
It was manufactured according to the process shown in FIG. 2 by using O ₃ and a stripe-shaped metal mask for forming a grating (grating period: 0.5 μm). Table 1 shows the compositions of the glasses A and B, the change rate ΔD (T) / ΔC of the change in the mutual diffusion coefficient with respect to the change in the Ag ion concentration ΔC in the glass, and the results (reflectance). Here, C is Ag ion in glass / (Ag ion + alkali ion concentration) ×
100, 5% to 10%. ΔD (T) is a value obtained by dividing the difference between the mutual diffusion coefficients when C at a temperature of 280 ° C. is 5% to 10% by the mutual diffusion coefficient of C = 5%.

[0022]

[Table 1]

The combination of glass A and Ag ions is ΔD
(T) /ΔC=0.1, and no light reflection occurred. On the other hand, in the combination of glass B and Ag ions, ΔD (T) /ΔC=0.35, and the reflectance is 60%.
Was obtained, and a grating was formed. As a result of further study, when ΔD (T) / ΔC was 0.2 or more, a grating could be formed.

[0024]

According to the present invention, as described above, the manufacturing process, the relationship between the glass substrate and the doped ion species, or the doped ion species is devised, and the ion exchange is performed using a stripe-shaped metal mask for forming a grating. Therefore, fine regions having different refractive indexes can be easily formed in the ion-exchange type embedded optical waveguide, and a grating having a desired fine period can be efficiently manufactured.

[Brief description of the drawings]

FIG. 1 is a process explanatory view showing an example of a first method of a method of manufacturing an optical waveguide grating according to the present invention.

FIG. 2 is a process explanatory view showing one example of a second method of the method of manufacturing the optical waveguide grating according to the present invention.

FIG. 3 is a process explanatory view showing an example of a third method of the method of manufacturing the optical waveguide grating according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Glass substrate 12 Metal mask for optical waveguide formation 14 Refractive index increasing part 16 Embedded optical waveguide 18 Metal mask for grating formation 20 Fine area by ion exchange

Continued on the front page. (72) Inventor Masaru Tosho 5-36-11, Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd. (72) Inventor Tatsushi 5-36-11, Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Inside (72) Inventor Yasuhiro Anma 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. (72) Inventor Junko Ishizu 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. F term (reference) 2H047 KA04 LA02 PA13 QA04 2H049 AA36 AA45 AA59 AA62

Claims (4)

[Claims] 1. A method for forming an optical waveguide grating in which an ion-exchange type optical waveguide is embedded in a glass substrate and the refractive index of which is changed at a predetermined period in a light propagation direction in the optical waveguide. A first ion exchange step of providing a metal mask for forming a waveguide pattern and performing thermal ion exchange; a step of removing the metal mask for forming an optical waveguide pattern; and an electric field for embedding the ion-exchanged refractive index-increased portion in a glass substrate. A second ion exchange step of performing an applied ion exchange to form a buried optical waveguide, providing a stripe-shaped grating-forming metal mask on the surface of the glass substrate, and applying a higher electric field while applying an electric field than in the first ion exchange. By performing ion exchange with ions of the third type, a third type of ion concentration distribution is periodically controlled without breaking the shape of the optical waveguide. -Exchange step, the step of removing the grating forming metal mask, comprises a method of optical waveguide gratings and forming a refractive index change of the minute periodic optical waveguide. 2. A method for forming an optical waveguide grating in which an ion-exchange type optical waveguide is embedded in a glass substrate and a refractive index of the optical waveguide changes in a predetermined period in a light propagation direction in the optical waveguide. A first ion-exchange step of selecting a combination of ions and glass having a strong ion concentration dependence of the mutual diffusion coefficient of the above and performing a thermal ion exchange by providing a metal mask for forming an optical waveguide pattern on the surface of a glass substrate; A step of removing the metal mask for pattern formation; a second ion exchange step of forming an embedded optical waveguide by performing electric field application ion exchange to embed the ion-exchanged refractive index increasing portion in the glass substrate; A metal mask for forming a stripe-shaped grating is provided, and thermal ion exchange is performed with ions having a higher concentration than in the first ion exchange. (3) an ion exchange step, a step of removing the grating-forming metal mask, and (3) an electric field application ion exchange for embedding a portion ion-exchanged in the third ion exchange step up to the optical waveguide portion, thereby changing the shape of the optical waveguide. A fourth ion exchange step of periodically controlling the ion concentration distribution without breaking down,
A method for manufacturing an optical waveguide grating, wherein a refractive index change with a fine period is formed in the optical waveguide. 3. A method for forming an optical waveguide grating in which an ion exchange type optical waveguide is embedded in a glass substrate and the refractive index of the optical waveguide changes in a predetermined period in the light propagation direction. Providing a metal mask for forming a waveguide pattern, performing ion exchange using a first ion in which ion exchange proceeds at a high temperature and does not proceed at a low temperature to form a buried optical waveguide, a stripe shape on the surface of a glass substrate Forming a fine region having a different refractive index in the optical waveguide by performing electric field application ion exchange using the second ion whose ion exchange proceeds at a low temperature. Forming a periodic refractive index change in the optical waveguide without breaking the optical waveguide. 4. The optical waveguide according to claim 3, wherein the first ion whose ion exchange proceeds at a high temperature and whose ion exchange does not proceed at a low temperature is a Tl ion, and the second ion whose ion exchange proceeds at a low temperature is an Ag ion. Grating manufacturing method.