JPH02259607A - Production of optical waveguide - Google Patents

Abstract

PURPOSE:To easily obtain the three-dimensional optical waveguides, etc., by adsorbing a dopant in a gaseous phase into the pores in porous glass controlled finely in a diffusion region. CONSTITUTION:The pores in the porous glass are previously positionally selectively closed 4, 5 by the polymer of a photopolymerizable compd. to limit the diffusion in a lateral direction. The porous glass is thereafter subjected to doping 6 by utilizing the multimolecular layer adsorption of the vapor of the dopant material to the pore surface of the porous glass. The porous glass is then rested in the atmosphere of the dopant partial pressure lower than the equil. pressure to partially desorb 7 the dopant. The dopant concn. of only the peripheral part of the glass is lowered to form a dopant concn. distribution 8 having the max. in the glass. The operation to fix the resulted dopant distribution in the form of an oxide into the pores is executed and further, sintering 9, 10 and pore elimination are executed, by which the desired optical waveguide parts 11 are formed in the glass. The three-dimensional (embedded type) optical waveguides are easily obtd. in this way.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing an optical waveguide.

[Prior art] A substance that changes the refractive index is introduced into a limited area inside the glass using a diffusion phenomenon to control the waveguide of light, creating three-dimensional (embedded) optical waveguides and other devices. Several techniques have been proposed in the past as techniques for realizing optical functional devices.

The first method is called the ion exchange method, in which a multicomponent glass containing exchangeable ionic components is immersed in a molten salt containing ions that increase or decrease the refractive index, and ion exchange (diffusion) is performed. By doing this, a refractive index distribution is realized (E, 0kuda et at, App
Lied 0ptics, 23.1747 (1984
)) o In this case, in order to create a so-called embedded type glass body in which a limited area inside the glass has the maximum refractive index, the surface of the glass substrate must be coated with metal vapor deposition, etc. before ion exchange. masking and limiting the ion diffusion region (L Oikawa etat, El
ectron, Lett, 17(3), 452(1
981)).

The second method is called the molecular stuffing method.
Porous glass was used as the substrate, and Cs was used as the dopant.
It is immersed in an aqueous solution containing monovalent ions such as + and Tl+, and the ions are diffused (stuffed) into the pores. After that, it is immersed in a suitable solvent and some of the ions are eluted (unstuffed) to form the desired refractive index distribution, then the ions are precipitated into the pores to fix the distribution, and then fired to make it non-porous. (Asahara, Ceramics, 21.425
(1986)). The method may also include introducing substances other than ions as dopants, for example in the form of oxide precursors such as metal alkoxides.

In this case, in order to create an embedded glass body, the pores inside the porous glass are regioselectively blocked with a photopolymerizable low-molecular compound to limit the diffusion area of ions and oxide precursors. (Japanese Unexamined Patent Publication No. 61-232)
248>.

[Problems to be Solved by the Invention] The first ion exchange method has advantages such as being able to form the refractive index distribution into a smooth parabolic shape close to the ideal.

However, operations such as heating are necessary due to the slow diffusion rate of ions in the solid phase, and even then, several hours are required to obtain the required distribution. Furthermore, since only the surface of the substrate is masked, there is also the influence of diffusion in the lateral direction, that is, in the direction perpendicular to the thickness direction. An electric field application method has been attempted as a method to shorten the diffusion time and promote embedding inside, but it requires complicated equipment and time, such as the need to mold the substrate into a box shape. The disadvantage is that it requires Furthermore, this method is limited to monovalent ions with high mobility and cannot be applied to highly charged ions. Furthermore, when considering compatibility with optical fibers, multi-component glass has high absorption and poor compatibility.

The second molecular stuffing method utilizes the diffusion of ions or oxide precursors in the liquid phase in the pores of porous glass, and because their diffusion rate is higher than in the ion exchange method, It is possible to form a refractive index distribution over a wide range in a relatively short time, and when combined with position-selective occlusion of pores, it is also possible to control diffusion on the order of tens of micrometers. It is. However, oxide precursors such as polyvalent metal alkoxides and chlorides (most of which are liquid at room temperature) are desirable as substances to be introduced into the pores.
Generally, they have high reactivity and are difficult to handle while still in the liquid phase. Further, fixation by oxidation is often carried out by utilizing thermal decomposition during sintering, but since volatilization from the pores occurs during heating, it has been extremely difficult to control the refractive index distribution.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, the pores in the porous glass are regioselectively blocked in advance with a polymer of a photopolymerizable compound, and the pores in the lateral direction are limit the spread of after that,
Porous glass is doped in the gas phase by utilizing multilayer adsorption of dopant substance vapor onto the surface of porous glass pores.

During doping, taking advantage of the property that the equilibrium adsorption amount depends on the dopant pressure, first, the entire unblocked pores are doped under an equilibrium pressure corresponding to the dopant amount that provides the desired maximum refractive index. Then, by leaving the dopant in an atmosphere with a dopant partial pressure lower than this equilibrium pressure and partially desorbing the dopant, the dopant concentration only in the peripheral area of the glass is reduced, forming a dopant concentration distribution with a maximum inside the glass. .

By fixing the dopant distribution obtained in this way inside the pores in the form of oxides, and then sintering and making the glass pore-free, a desired optical waveguide portion is formed inside the glass.

By using the present invention, a three-dimensional (embedded) optical waveguide can be easily manufactured using a simple device and operation.

The lateral diffusion of the dopant gas is controlled by position-selective occlusion of the pores, so if this occlusion is carried out minutely, the lateral direction will consist of equally fine doped and non-doped sections. It is possible to form a pattern of dopants. In this case, if exposure is performed using a photomask, it is possible to form a fine pattern on the order of several tens of micrometers.

Photopolymerizable compounds are particularly restricted as long as they can be uniformly filled into the pores of porous glass in a short time, are easily photopolymerized, and the polymer is easily decomposed and removed by heating. It is possible to use general photopolymerizable low molecules instead of those used in conventional photopolymerizable polymers. For example, organic low molecules such as acrylic acid, methacrylic acid, styrene, and derivatives thereof are particularly easy to handle and convenient. In addition, in order to increase light absorption efficiency during photopolymerization, improve pattern clarity, and shorten exposure time, photodegradable compounds called photoinitiators, photosensitizers, etc. are added to photopolymerizable compounds. It is good to add a small amount to.

Since the amount of dopant can be controlled by the equilibrium adsorption amount determined by the dopant pressure and temperature in the atmosphere, it is possible to control the maximum value of the refractive index difference with this equilibrium adsorption amount. however,
The dopant must be a compound with a vapor pressure sufficient to provide the amount of adsorption necessary to produce the desired refractive index difference. Typical dopant substances include metal halides, alkoxides, hydrides, carbonyl compounds, etc., but are of course not limited to these. It is also conceivable to use a mixture of these gases or to dilute with a suitable gas such as He or N2.

In order to leave the porous glass in an atmosphere with a dopant pressure lower than the equilibrium adsorption pressure and partially desorb the dopant near the surface through the glass surface, for example, the dopant pressure is reduced to a predetermined value using a vacuum pump. Methods such as replacing with another gas can be used. The dopant concentration distribution is determined by the balance between the diffusion inside the glass and the speed of desorption from the surface, so it is possible to form a square distribution etc. by appropriately selecting the pressure and standing time during desorption. . In addition, if doping is carried out to the limit where the pores are all occupied by the dopant, the dopant inside the pores will be in a so-called liquid phase state, and especially in the early stage of vapor phase desorption, the dopant will be in a gas-liquid state inside the porous glass. It evaporates while forming an interface. Therefore, if desorption is completed during evaporation, compared to not doping to the limit,
It is also possible to form a steeper refractive index distribution based on the gas-liquid interface.

The rate at which the dopant is adsorbed and desorbed is extremely high because it is doped in the gas phase, and a region exhibiting a maximum dopant concentration can be quickly formed inside the glass.

In the vapor phase doping method, doping, including drying and desorption of porous glass, is performed in a vacuum line, so that the process of removing adsorbed water in pores that inhibits diffusion and the formation of distribution by doping are completely the same. can be performed as a series of operations on the line. At this time, various highly reactive dopants can be stably and safely used without being diffused to the outside.

Hydrolysis, oxidation with gaseous oxygen, or the like may be used to fix the dopant distribution in the pores. In the former case, methods such as immersing the porous glass in water or introducing it into a vacuum line in the form of water vapor are possible, and both methods are extremely easy to implement. At this time, since the formed distribution is not disturbed, the higher the hydrolysis rate of the dopant is, the more advantageous it is, and it is possible to use various methods to increase the rate, such as performing hydrolysis in warm water.

[Example] The following description will be made with reference to examples.

Example 1 Bulk density 1.7g/cm", specific surface area 400m37g1
A flat porous glass with a thickness of 1 mm was heated at 150°C in a vacuum.
Figure 1 (a)) was heated for 1 hour to remove adsorbed water and then returned to room temperature.
It was immersed in the liquid for 5 hours ((b)). This glass is taken out, placed in the air with a glass photomask with a pattern made of metallic chrome, and exposed to ultraviolet light.
The MA in areas other than those shielded by the mask pattern was photopolymerized ((C)). Thereafter, unpolymerized MA was removed from the light-shielded area by the pattern by leaving it in a vacuum at room temperature for 30 minutes, and then at 100°C for 30 minutes.
d)). Through the above steps, the pores were partially blocked.

This glass was placed in a vacuum line, and after the entire line was evacuated, germanium tetrachloride (GeC1<) vapor was introduced and adsorbed into the pores until equilibrium was reached ((e)). The final equilibrium pressure at that time was 40 torr, and it took about 2 hours to reach equilibrium. Next, the system was evacuated to bring the atmosphere around the porous glass to approximately 0 torr, and a portion of the adsorbed GeC1 was allowed to desorb through the glass surface for 5 minutes ((f)).

This porous glass was taken out from the vacuum line and immersed in pure water at 25° C. for 4 hours to hydrolyze Ge Cl 4 and fix it as GeO 2 ((g)). Then, it was taken out of the water, dried at room temperature ((h)), and then heated to 1000°C in an electric furnace. This heating decomposes and evaporates the MA that had photopolymerized and blocked the pores (see (i)
), and the pores were made non-porous by further heating (same (j)).

When observing the cross section of the sample thus obtained, it was found that a region with a high refractive index due to G e O 2 was formed inside the glass.

Comparative Example 1 A glass containing GeC2 was produced in the same manner as in Example 1 except that partial pore closure and dopant desorption were not performed.

When the cross section of the obtained sample was observed, the refractive index increased almost uniformly throughout the sample, and the glass was optically uniform.

[Effects of the Invention] According to the present invention, by adsorbing a dopant in the gas phase into the pores in a porous glass whose diffusion region is finely controlled, high-density particles can be easily and precisely added to the interior of the glass. A region of refractive index can be formed. Therefore, it is possible to easily produce three-dimensional optical waveguides, etc., and various applications in the field of optoelectronics are expected.

[Brief explanation of drawings]

FIG. 1 shows a cross section of the glass in each step of Example 1. 1 ... Porous glass 2 ... Porous glass impregnated with photopolymerizable low molecules 3 ... Photomask 4 ... Polymerization region of low molecules by ultraviolet rays 5 ...
Region 6 from which unpolymerized low molecules are removed...A region from which dopants are adsorbed by vapor phase doping? ... Part 8 where the dopant near the surface has been desorbed... Part 8 where the dopant has been fixed by hydrolysis etc. (particularly water has entered near the surface) 9 ... Part where water etc. has been removed 10... When the polymer was removed by thermal decomposition 11... Glass made non-porous by heating Patent applicant Mitsubishi Gas Chemical Co., Ltd. Representative Patent attorney Sadafumi Kobori (a) [111 Figure 1

Claims (1)

[Claims] (1) a step of blocking some of the pores in the porous glass with a polymerizable compound; (2) a step of introducing and fixing a dopant into the unblocked pores of the porous glass;
3) a step of decomposing and removing the polymerizable compound; and (4) a step of baking the porous glass to make it non-porous. Some of the pores in the porous glass are blocked by regioselective photopolymerization, and the dopant is introduced in the gas phase into the unblocked pores until an adsorption equilibrium is reached, and then the surrounding area of the glass is removed by vacuum desorption. A method for manufacturing an optical waveguide, comprising: lowering the concentration of the dopant in the pores, and then fixing the dopant in the pores.