JPS60191208A - Optical circuit element and its production - Google Patents

Abstract

PURPOSE:To obtain an optical waveguide which has optional spread from a visible part to an IR region with less light loss by diffusing potassium as a dopant on a glass substrate and forming a glass film thereon then diffusing again the potassium. CONSTITUTION:An Al layer 4 including a groove 6 is formed on a glass substrate 1 contg. Na ion and is immersed in molten KNO3 7 to diffuse K ions into the part of the groove 6. A glass film 2 is formed by RF sputtering on the substrate 1. The substrate 1 is heated to diffuse again the K ion, thus forming a diffused region 3 having a high refractive index. The diffused region 3a having ununiform spread is also formable by using a carbon dioxide laser and performing locally distributed heating. The optical waveguide having optional spread from the visible part to IR part with less light loss is thus obtd.

Description

Detailed Description of the Invention (7) Technical Field The present invention relates to an optical circuit element used in an optical integrated circuit and having a waveguide that is not necessarily uniform along the direction of propagation, and a method for manufacturing the same.

The waveguide structure conventionally used in optical integrated circuits is one in which the refractive index is locally increased by doping a part of a dielectric or semiconductor with impurities, and the waveguide structure is made by doping a part of a dielectric or semiconductor with impurities to locally increase the refractive index. It was a wave path.

Waveguides of uniform width are combined or branched to perform various functions.

However, branch circuits with low radiation loss, high efficiency laser fiber couplers, or single mode optical fiber
In order to realize thin-film optical circuit coupling, etc., a waveguide structure that is not necessarily uniform in the propagation direction is required.

Establishment of technology for fabricating circuits in which waveguide parameters change over short distances from 1 to 100 times the wavelength of light along the propagation direction, and optical three-dimensional circuit technology to realize new circuit functions. or desired.

(B) Prior art The present inventor diffused silver ions into glass and changed the degree of diffusion by changing the temperature in the waveguide direction, thereby creating a leading waveguide with a varying width. Created.

This waveguide and its manufacturing method were presented at the 1983 National Conference of the Institute of Electronics and Communication Engineers (March 1983, lecture number 1078, Proceedings, pages 4-164).

This is done by applying an appropriate mask to the borosilicate crow and (lth
It is immersed in an acid #melt solution to perform diffusion to replace the Na+ ions in the glass with Ag+ ions, which is then further heated and re-diffused. When heating, do not heat it uniformly, but with a distribution. Re-diffusion progresses quickly in strongly heated areas, while re-diffusion progresses slowly in weakly heated areas, making it possible to manufacture waveguides with different widths in the direction of propagation.

In this way, for example, mode matching elements, optical branches, etc. can be created.

In practice, after silver is diffused into a glass substrate, the same glass is attached to the surface by sputtering, and the waveguide is embedded in the glass. When heated to re-diffuse the silver ions, they enter the substrate, but also into the glass coating.

As the re-diffusion progresses, the concentration of silver ions expands in an elliptical shape. The higher the re-diffusion temperature and the longer the time, the wider the isothermal curve becomes, moving from an ellipse to a circle. Therefore, by changing the re-diffusion temperature or time in the direction of propagation, optical waveguide structures with different widths in the direction of propagation can be obtained.

However, the silver-diffused optical waveguide had the following drawbacks.

(1) Disadvantages of silver-diffused waveguides If a waveguide in which silver is diffused is directly embedded by RF sputtering, yellow-brown coloring occurs in the silver-diffused portion, increasing loss in the visible range.

This is thought to be due to colloidal formation of silver ions in the glass. The cause of colloid formation is thought to be that silver ions are reduced by the high thermal energy -t'- of the sputtered particles during RF sputtering and high-speed secondary electrons from the target, resulting in amorphous formation.

←) Optical waveguide of the present invention In the present invention, instead of using silver ions as a dopant, potassium ions are used as a dopant to produce a leading waveguide.

The glass is composed of Si, B, A# acid f arsenides, and Ba, Na, etc. oxides as network modifying oxides. The concentration of Na oxide varies depending on the glass. However, in a certain glass, the concentration of Na oxide is constant, and therefore the refractive index is constant within the glass.

On the other hand, when ions are locally doped and replaced with Na ions, the electronic polarizabilities of K ions and Na ions are different, resulting in locally different refractive indexes. When K ions are doped into glass, they increase the dielectric constant, thereby increasing the refractive index and thus making it possible to form an optical waveguide.

The F3A of the present invention is characterized in that potassium is used as a dopant to diffuse into glass, and an optical circuit having an arbitrary distribution can be produced by re-diffusion.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

The substrate and the glass must satisfy the following conditions.

(1) It is possible to fabricate a diffused waveguide.

(2) It is possible to form a thin film with low loss by sputtering.

(3) It has a small coefficient of linear expansion and can withstand local heating.

(4) Network-modifying oxide in glass) Since the refractive index is increased by replacing IJ with potassium, the Na2O concentration must be high to some extent.

Tempax (Tempax) satisfies these conditions.
pax), Microsheet
There is a meaning.

Table 1 shows their compositions and physical properties.

Hereinafter, a method for manufacturing an optical waveguide according to the present invention will be explained.

Table 1 Composition and physical properties of glass (Tsukuda in the composition is expressed in +'%% by weight of a 12ft object or is abbreviated using elements other than glass.) In the present invention, sodium in the glass is replaced with potassium. , a locally high refractive index region is formed, and this is used as an optical waveguide. Therefore, in the following explanation, the potassium diffusion region may be referred to as a high refractive index region or an optical waveguide.

First, an aluminum mask is formed on a glass substrate. For this purpose, a normal photolithography method is used.

Figure 1 shows the state after an aluminum layer 4 is vapor-coated on a glass substrate 1, a resist 5 is further applied, this is exposed using a mask with a waveguide pattern, and the resist is developed. FIG.

Here, a portion of the resist where a waveguide is to be formed is removed, leaving a groove 6. Although a straight groove 6 is shown here, it may have any shape.

Next, the resist 5 is removed using acetone or the like.

An aluminum layer 4 remains on the substrate 1.

Next, the process of ion exchange begins. This is done by soaking in molten KNO37 at a suitable temperature for a suitable period of time. FIG. 2 is a perspective view showing this.

The temperature is controlled in an electric furnace and ions are exchanged. This is to diffuse potassium in KNO3 into the glass substrate 1, and in case 6 without the aluminum layer 4,
It is replaced by potassium or lithium in glass.

I am using 100% KNO3 molten salt, but KNO3
A mixed solution of NaN03 and NaN03 may be used as a sacrificial salt.

Diffusion temperature is 400-470'C1 Diffusion time is 20-80'C
It's time.

The melting point of KNo 3 is 333°C. At temperatures above 350°C, nitrite gas is generated. For this reason, diffusion is performed while evacuating the inside of the electric furnace.

FIG. 3 is a perspective view of the crow after diffusion, and a diffusion region 3 in which potassium has been diffused is formed in the groove 6 (indicated by a dot).

After ion exchange (diffusion), the glass is washed with water and dilute nitric acid to remove KNO3 adhering to the substrate (4).Furthermore, it is immersed in Esotynda solution to remove the aluminum layer 4 of the mask.
remove.

FIG. 4 shows this state.

In this state, the diffusion region 3 is exposed, so the surface is coated with glass, which is the same material as the substrate, and the diffusion region 3 is buried.

The embedding is performed by RF sputtering.

Tenbatuskusnolas is deposited on the surface where the diffusion region 3 is provided by RF sputtering.

By sputtering, the glass coating 2 is deposited on the substrate 1 by approximately 2
It should be formed to have a thickness of 0 to 30μ771.

Spackling is performed while introducing an argon gas into the container at a pressure of 5 to 5 Pa. RF power was 100W. The deposition rate of the film by sputterlink' is 0.
It was 6-0.7 μm/Hr.

The sputtered coating 2 may become colored. This is because the temperature of the glass substrate becomes too high and some oxides decompose and become visible light absorption sources.

To avoid this, it is recommended to improve the heat dissipation of the glass substrate and spankling it. The inventor applied grease between the holder of the spankling device and the substrate in order to improve heat dissipation. In this way, the coating 2 will not be colored.

FIG. 5 is a perspective view of a state in which the diffusion region 3 is embedded with the cover 1 and the cover 2. FIG.

Next, the substrate 1 is heated to re-diffuse potassium ions. This may be due to uniform heating or distributed heating.

Uniform heating is heating the entire substrate 1 and film 2 to the same temperature to uniformly re-diffuse the dopant. 6th
The figure is a perspective view of a -j-shaped waveguide formed by uniform heating.

In the case of uniform heating, the substrate is placed in an electric furnace and re-diffused. The temperature is around 400°C and the re-diffusion time is 1-5.
It is about hr.

Due to re-diffusion, the flat diffusion area expands in the vertical direction,
Forms a thick waveguide.

Rediffusion has the effect of not only enlarging a region with a high refractive index but also reducing loss in the waveguide portion.

For example, an optical waveguide that had a loss of 5.2687 cm before rediffusion became an optical waveguide with a low loss of 1.5 dν by rediffusion treatment at 400'C and 1.5 hours.

Distributed heating is not heating at a uniform temperature along the length of the diffusion region, but heating with a temperature distribution.

In high-temperature areas, re-diffusion progresses quickly, so the diffusion region with a high refractive index becomes wider. In the low temperature region, re-diffusion proceeds slowly and the diffusion region remains narrow.

FIG. 7 is a perspective view of a circuit element in which diffusion regions (high refractive index regions) 3a to 3b having different widths are re-diffused by distributed heating.

In the front diffusion region 3a, diffusion is carried out at high temperature, so
Potassium ions spread far from their initial position. Since the rear diffusion region 3b is kept at a low temperature, re-diffusion hardly progresses.

Heating so that the temperature varies along the length of the diffusion region is called distributed heating. To perform distributed heating,
It is no longer possible to use electric furnaces.

In order to achieve distributed heating, it is necessary to use a heat source that can locally concentrate and supply energy.

The inventor used a carbon dioxide gas laser as a heat source for local heating.

The light of the carbon dioxide laser is transmitted over a short distance within the power laser.
(20-30μ〃1), and can be narrowed down as necessary, allowing for waveguide shaping with a large degree of freedom.
jf is capable.

A carbon dioxide laser beam is scanned along the waveguide.

Rather than uniformly scanning the waveguide, the scanning speed, number of scans, and laser power are varied depending on the position on the waveguide, creating a temperature distribution along the waveguide and changing the rate of re-diffusion.

The inventor of the present invention changes the laser light irradiation time (that is, the re-diffusion time) along the waveguide by changing the number of scans.

A laser beam is scanned from one point on the waveguide as a starting point. When the scanning distance is changed stepwise to widen the scanning range, a gradient of irradiation time occurs on the waveguide.

Let me give an example. Laser power is 2W, scanning speed is 160
It is assumed to be μm/sec. From the starting point, the scanning range is 2.0 mm,
2.2 fins, 15 each with 6.4 fins and approximately 0.2 fins
Set V to the stage. Each stage is scanned repeatedly 20 times. A total of 300 scans will be performed. The irradiation time is the longest at the starting point, and the irradiation time becomes shorter as you move away from the starting point.

In this way, the distributed heated sample is heated from the starting point to l# scrap, I
It was cut at the IJFJI point, and the distribution of potassium ions on the cut surface was measured using EPMA.

FIG. 8 is a distribution diagram showing the potassium distribution in a cut plane 11 mm from the starting point. A high concentration (5 wt %) potassium ion distribution remains near the boundary between the substrate 1 and the coating 2. This means that no re-diffusion has occurred.

Furthermore, it was found that potassium did not enter into the coating 2 which was applied by sputtering after potassium was diffused into the glass by KNO3.

FIG. 9 is a potassium distribution diagram at a cross section one distance from the starting point. Potassium is re-diffused vertically, horizontally, and even into the coating 2, as represented by an elliptical isoconcentration curve. Furthermore, a particularly high concentration portion (5 wt%) has disappeared. Potassium diffuses around the periphery, reducing the concentration in the center.

In this way, the high refractive index region in the glass, ie the region of the optical waveguide, is expanded. The horizontal symmetry and vertical symmetry are also good.

0゛) Change in Potassium Concentration To investigate the effect of re-diffusion, the potassium concentration in the thickness direction of the glass was measured by EPMA. Figure 10 shows the potassium concentration (K2O wt%) in the substrate and film before re-diffusion.
). The horizontal axis indicates the distance in the vertical direction with the origin at the interface between the substrate and the coating, and the vertical axis indicates the distance in the 20 w
t%. The thickness of the coating is 6.5 μm.

Before re-diffusion, a maximum potassium concentration of 5% was detected at a depth of 2-3 μm from the interface. A potassium concentration also appears in Coating 2, which is at a concentration of 20% originally contained in Tempax glass.

Tempax glass contains just under 1% of 20.

The 11th graph is a graph showing the measurement results of the potassium concentration in the thickness direction of the substrate and coating after re-diffusion at 400°C for 2 hours. The maximum potassium concentration in the substrate 1 has decreased. Instead, it can be seen that potassium is diffused into the substrate at a depth of about 10 μm from the boundary.

Furthermore, it can be seen that potassium diffuses into the 1 to 2 μm thick portion within the film.

FIG. 12 is a graph showing changes in potassium concentration (-20) in the thickness direction of the substrate and the coating after re-diffusion at 400°C for 8 hours.

It can be seen that the maximum potassium concentration within the substrate further decreases, and potassium enters into areas with a depth of 10 μm or more. In the film, potassium diffusion progresses to about 3.5 μm from the boundary.

In this way, the distribution approaches a bilaterally symmetrical distribution regardless of the substrate or coating with respect to the point giving the maximum value of potassium Aa degrees.

(Force) Birefringence and Potassium Concentration The optical waveguide fabricated in this way is one in which sodium ions in the glass are replaced with potassium ions.

Therefore, it is tentatively called a sodium-potassium ion exchange waveguide.

A distinctive feature of sodium-potassium (written Na-) ion exchange waveguides is significant birefringence. This is a property not found in materials doped with silver ions.

The refractive index NtO for light having a polarization plane perpendicular to the diffusing portion of the sample is larger than the refractive index Np for light having a polarization plane parallel to the plane. The difference in refractive index between the two at the surface is 7×
It is 10.

Furthermore, the difference in refractive index between the diffusion region that becomes the waveguide and the substrate glass increases in proportion to the amount of potassium doped;
A sample subjected to diffusion (in a KNO3 melt) at 470°C for 32 hours had a density of about 3.5 x 10 .

When potassium ions are diffused and distributed inside the sample by re-diffusion, the maximum value of birefringence decreases and the region where birefringence appears expands.

After all, it is thought that the refractive index change obtained by K-Na ion exchange and the birefringence correspond well to the dopant concentration.

(g) Effects (1) After diffusion and embedding, re-diffusion is performed, and the re-diffusion temperature,
By locally varying the time, it is possible to create a leading wavepath with any desired spread.

(2) Those doped with silver ions have a high loss in visible light and cannot be used as optical circuit elements for visible light. The material of the present invention has low loss from visible light to infrared light. Therefore, it is effective as an optical circuit element for infrared light and visible light.

For example, although ion exchange (diffusion) was performed in KNO3 at 450°C for 19 hours, 450°C for 25 hours, and 420°C for 30 hours, and a film was applied by sputtering, HeN
The loss for e light is 4.1 dB/l-m, 2.6
dB/z, 2.9 dB. By re-diffusion,
Losses are further reduced.

For example, at 400″G, 8 hours of respreading, 2.9 dB
/c1n sample loss was reduced to less than 1 dB/a.

Applications According to the present invention, it is possible to provide an optical waveguide structure in which the waveguide width and thickness gradually change along the propagation direction of light.

(i) Mode matching device between semiconductor laser and optical fiber (2
) Can be applied to mode matching devices between optical fibers and thin film optical circuits.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the state after an aluminum layer and a resist are attached to a glass substrate, exposed to light using an appropriate mask pattern, and developed. FIG. 2 is a perspective view showing a state in which the resist has been removed and the glass substrate, which is masked except for the region to become a waveguide, is being subjected to ion exchange (diffusion) in molten KNO3. FIG. 3 is a perspective view showing a state in which a region in which potassium ions are diffused is formed after the expansion 11t. FIG. 4 is a perspective view of a glass substrate from which aluminum has been removed. A diffusion region (of potassium) is formed in the portion that will become the waveguide. FIG. 5 is a perspective view showing a state in which the same type of glass is deposited on the upper surface of the substrate 1 by sputtering to form a film and embed a diffusion region. FIG. 6 is a perspective view showing the uniform spread of the diffusion region after the substrate 1 and coating 2 are uniformly heated and rediffused after the embedding process. FIG. 7 is a perspective view showing a state in which distributed heating is performed by varying the temperature or time in the longitudinal direction of the waveguide during the embedding process to produce a guiding waveguide whose width and thickness vary in the longitudinal direction. FIG. 8 is a distribution diagram of potassium concentration (wt% of K2O) in the longitudinal section of the substrate and film in the unheated portion when re-diffusion is performed by distributed heating as shown in FIG. FIG. 9 is a distribution diagram of potassium concentration (wt% of K2O) in a vertical cross section of the substrate and film in a region where heating is actively performed when re-diffusion is caused by distributed heating as shown in FIG. Figure 10 shows the potassium concentration (K) of the substrate and film before re-diffusion.
Graph showing measured values of 2O wt%). The horizontal axis is the depth from the boundary between the substrate and the film, μ? ? 1) is shown. Vertical axis is 20
This is 1% per ton. The thickness of the coating is 6.5 μn+. Figure 11 shows the substrate after re-diffusion at 400°C for 2 hours.
Graph showing the measured potassium (K2Owt%) concentration in the direction perpendicular to the plane of the coating. Figure 12 shows the substrate after re-diffusion at 400'C for 8 hours.
m Potassium in the direction perpendicular to the IFJO plane (K2Owt%
) Graph showing concentration measurements. 1 Crow Substrate 2 ・ Broken membrane 3 ・ Diffusion region, optical waveguide, high refractive index region 4 ・
・ Aluminum layer 5 ・ ・ ・ Groove

Claims (2)

[Claims] (1) A glass substrate 1 containing sodium in which potassium ions are diffused in the position where a leading waveguide is to be formed, a glass coating 2 formed on the glass substrate 1, and a glass substrate 1 containing potassium ions diffused in the glass substrate 1. , a substrate 1 and a leading waveguide 3 formed by re-diffusion into a coating 2. (2) A mask pattern having grooves 6 at positions where optical waveguides are to be formed is formed on the surface of the glass substrate 10 containing sodium, and the glass substrate 1 is immersed in a melt containing KNO3 to form a potassium ion diffusion region along the grooves 6. A coating 2 is deposited on the glass substrate 1 to fill the diffusion region 3 by sputtering glass of the same phase.
Manufacture of an optical circuit element characterized by uniformly or distributed heating of the film 2 to re-diffuse potassium ions to form a leading waveguide whose width, thickness, and refractive index vary uniformly or longitudinally. Method.