JP2001108851A - Optical waveguide grating and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively and easily form a grating with good accuracy at a desired submicron period without dependence upon polarization in an optical waveguide of an ion exchange type. SOLUTION: Portions where metal ions are deposited in a colloidal state and portions where the metal ions exist in the state of an ion state are arrayed alternately periodically in the ion exchange type optical waveguide formed in a glass substrate, by which refractive index changes are generated at a specified period. The metallic particulates deposited in the colloidal state are formed Ag colloid. The period of the refractive index changes is preferably specified to 0.2 to about 1.0 μm. The entire part is irradiated with the light of low-irradiation intensity to deposite the metal ions in the colloidal state and is then locally irradiated with the light of high-irradiation intensity at a desired period to eliminate the deposition. Otherwise, the portions are locally irradiated with the light of low-irradiation intensity at a desired period to deposite the metal ions in the colloidal state. As a result, the deposited portions and the portions in the state of the ion state are alternately periodically formed to give rise to the refractive index changes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical waveguide formed on a glass substrate by an ion exchange method, wherein a portion where metal ions are precipitated in a colloidal state and a portion where a metal ion remains in an ionic state are alternately and periodically. The present invention relates to an optical waveguide grating in which the refractive index changes at regular intervals, and a method for manufacturing the same. This technique is useful for an ion-exchange type 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 ion exchange, and is a low-temperature process (about 250 to 350 ° 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, and a high-temperature process (1200 to 130
(About 0 ° 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 is formed that selectively reflects only wavelength components close to the wavelength 2nΛ and transmits light of other wavelength components with low loss. 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, a planar waveguide type optical circuit using the ion exchange method is easy and inexpensive to manufacture, but an effective method for accurately manufacturing a grating having a small period in the optical waveguide has not yet been developed.

An object of the present invention is to provide an optical waveguide grating that produces a desired change in the refractive index at a fine period in an ion exchange type optical waveguide. Another object of the present invention is to
It is an object of the present invention to provide a method for easily and inexpensively forming a grating with a desired sub-micron period at low cost without any polarization dependence in an ion-exchange type optical waveguide.

[0009]

Means for Solving the Problems The present inventors irradiate a glass substrate with a certain light to a refractive index increasing portion formed by an ion exchange method, and increase the refractive index in accordance with the irradiation intensity. Ions precipitate in a colloidal state,
It has been found that the precipitation disappears and that the refractive index can be controlled thereby. The present invention has been made based on knowledge of such a phenomenon.

According to the present invention, a portion where metal ions are precipitated in a colloidal state and a portion where a metal ion remains in an ionic state are alternately and periodically arranged in an ion exchange type optical waveguide formed on a glass substrate. This is an optical waveguide grating in which the refractive index changes at a constant period.

As the glass substrate, for example, a glass material containing Na ions is used, and as the ions for increasing the refractive index forming the ion exchange type optical waveguide in the glass substrate, for example, Ag ions are used. In that case, the metal fine particles precipitated in a colloidal state are Ag colloids. The period of the refractive index change is, for example, about 0.2 to 1.0 μm.

The method of the present invention controls the disappearance of the metal fine particle deposition portion and the deposition of the metal fine particles by changing the intensity of light applied to the optical waveguide to cause a change in the refractive index of the optical waveguide. There is.

The first method is to form an optical waveguide on a glass substrate by an ion exchange method, irradiate the entire surface with light having a low irradiation intensity to precipitate metal ions in a colloidal state, and then apply the light having a high irradiation intensity locally. By irradiating at a desired period and eliminating the above-mentioned precipitation, a portion where metal ions are precipitated in a colloidal state and a portion where the metal ion remains in an ionic state are alternately and periodically formed. This is a method for manufacturing an optical waveguide grating that causes a change in the refractive index.

The second method is to form an optical waveguide on a glass substrate by an ion exchange method, locally irradiate low-intensity light with a desired period, and precipitate metal ions in a colloidal state. This is a method for manufacturing an optical waveguide grating in which a portion precipitated in a colloidal state and a part existing in an ionic state are alternately and periodically formed, thereby causing a change in the refractive index at a constant period.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS When light is applied to an ion-exchange type optical waveguide, a portion where metal ions are precipitated in a colloidal state and a portion where the metal ion remains in an ionic state can be formed in accordance with the intensity of the irradiated light. In order to irradiate a minute portion of the optical waveguide with light having a desired period, for example, there is a method of irradiating with interference fringes by laser light separated into two light beams. There is also a method of irradiating with interference fringes by laser light diffracted by a phase mask. These are the same methods as employed in forming a conventional fiber grating. Alternatively, there is a method in which a glass substrate is patterned with a metal having a desired period and irradiated with light.

As the irradiation light, visible light or ultraviolet light on the short wavelength side is used, and for example, light having a wavelength of 200 nm to 600 nm is preferable. When a glass material containing Na ions is used as the glass substrate and Ag ions are used as ions for increasing the refractive index for forming the ion-exchange optical waveguide, the irradiation light intensity is about 600 mW / cm ² , Above that, no precipitation occurs, below which precipitation occurs. By setting the precipitated particles to several hundreds nm or less, the communication wavelength is 1 to 1.7.
No loss occurs in the μm band. In such a deposited portion, the refractive index increases in the communication wavelength band, so that a periodic refractive index change can be obtained, and a grating can be formed.

[0017]

EXAMPLE Soda lime glass was used as a glass substrate and immersed in a molten salt of AgNO ₃ at 280 ° C. for 6 hours.
The entire surface of the substrate was subjected to ion exchange between Na ions and Ag ions. The glass substrate was subjected to an electric field application ion exchange treatment in a molten salt of NaNO ₃ at 280 ° C. and an electric field strength of 150 V / mm for 2 hours. Then, the glass substrate was irradiated with ultraviolet light. The irradiation beam diameter is 10 mm, and the irradiation intensity is 1200 mW / cm ² at the maximum. The intensity profile of the irradiation beam is shown in FIG. As shown in FIG. 1B,
Ag deposition portions 12 were formed in a ring shape on the glass substrate 10 in accordance with the irradiation intensity distribution. When compared with the intensity profile of the irradiation beam, the Ag deposition portion 12 was almost 600 mW /
cm ² is less area, 600 mW / cm in the ^two or more regions not occur the precipitation of Ag. This can be determined from the fact that yellow coloring can be observed in that region with the precipitation of Ag.

When the transmission spectrum is measured, as shown in FIG. 2, in the Ag deposition portion 12 (measured at the position (a) in FIG. 1B), surface plasmon absorption by the Ag colloid is observed at a wavelength of about 450 to 500 nm. I could observe it. But,
In the irradiated portion of 600 mW / cm ² or more (measured at the position (b) in FIG. 1B), absorption by Ag disappears in the transmission spectrum. The lower limit of the irradiation intensity at which the precipitation of Ag fine particles occurred was 50 mW / cm ² . The wavelength of the irradiation beam used was 365 nm. Measurement of transmission characteristics is diameter 1
Performed in a narrow area of mm. The precipitated Ag fine particles have a particle size of several tens.
It is a nanocrystal of nm and does not cause reflection or absorption, but changes in the refractive index occur.

As is apparent from the above embodiment, since the precipitation and disappearance of the metal fine particles can be changed in accordance with the irradiation light intensity, the desired irradiation intensity can be controlled by controlling the selection of the irradiation light intensity and the irradiation area and irradiation position. A grating with a fine period can be formed.

[0020]

As described above, according to the present invention, a portion where metal ions are precipitated in a colloidal state and a portion where the metal ions remain in an ionic state in an optical waveguide are formed alternately and periodically. Accordingly, an optical waveguide grating having no polarization dependence can be obtained.

In the present invention, since the precipitation and disappearance of fine particles can be controlled by controlling the intensity of irradiation light, an interference method or a mask method can be used for ultraviolet light irradiation, and a grating having a desired submicron period can be used in an optical waveguide at low cost. It can be easily formed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a relationship between an irradiation beam intensity profile and an Ag deposition portion formed on a glass substrate.

FIG. 2 is an explanatory diagram showing an example of a transmission spectrum.

[Explanation of symbols]

 10 Glass substrate 12 Ag deposition part

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuhiro Anma 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd. (72) Hiromitsu Umezawa 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electrochemical Co., Ltd. F-term (reference) 2H047 LA02 PA13 PA30 QA04 RA00 TA43

Claims (6)

[Claims] 1. An ion-exchange type optical waveguide formed on a glass substrate, wherein portions where metal ions are precipitated in a colloidal state and portions where metal ions remain in an ionic state are alternately and periodically arranged. An optical waveguide grating wherein a refractive index change occurs at a constant period. 2. The optical waveguide grating according to claim 1, wherein the fine metal particles precipitated in a colloidal state are Ag colloids. 3. The period of change in the refractive index is 0.2 to 1.0 μm.
The optical waveguide grating according to claim 1, wherein 4. An optical waveguide is formed on a glass substrate by an ion exchange method, and the entire surface is irradiated with light having a low irradiation intensity to precipitate metal ions in a colloidal state. By irradiating the above and eliminating the above-mentioned precipitation, a portion where the metal ion is precipitated in a colloidal state and a portion where the metal ion remains in the ionic state are alternately and periodically formed, whereby the refractive index change at a constant period is formed. A method for manufacturing an optical waveguide grating, comprising: 5. An optical waveguide is formed on a glass substrate by an ion exchange method, and low-intensity light is locally irradiated at a desired period to deposit metal ions in a colloidal state, whereby the metal ions are deposited in a colloidal state. A method of manufacturing an optical waveguide grating, comprising: forming periodically formed portions and portions that remain in an ionic state alternately and periodically, thereby causing a periodic change in refractive index. 6. The method of manufacturing an optical waveguide grating according to claim 1, wherein irradiation light having a desired period is formed by using interference fringes formed by laser light separated into two light beams.