JPH067206B2 - Method of manufacturing optical waveguide - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for forming an optical waveguide on a substrate such as glass. In particular, it is intended to form a refractive index square distribution type optical waveguide having a good coupling property with a graded index type (GI) optical fiber.

This optical waveguide is a transmission component for optical communication, an optical I
C, optical sensor components and the like, and can be widely applied to manufacturing technologies such as optical communication and optical applied measurement control.

Here, the refractive index squared distribution means that the refractive index of the core is the highest on the center line of the core and the distance r
It means that the refractive index decreases in proportion to the square of and becomes the same as the refractive index of the cladding at the boundary. The optical fiber is classified into a step index type (SI) type in which the core has a constant refractive index, and a graded index type (GI) in which the core refractive index is squared. The present invention intends to provide an optical waveguide having a good coupling property with a GI type optical fiber.

Glass is silica SiO ₂ with metal ions Na ⁺ , K ⁺ , Pb ⁺ ,…
Etc. are included. The refractive index is extremely low when only SiO ₂ is used. When metal ions are added to this, the refractive index increases in proportion to the concentration. Metal ions have electronic polarizability. Since the ions exist in an arc in SiO ₂ , the polarizability as a whole is given as the sum of these polarizabilities. Na ⁺
When some of the ions are replaced by metal ions of higher polarizability, the difference in polarizability times the total polarizability by the amount of substitution. Polarizability α is dielectric constant ε and ε = 1
It has a relationship of + 4πα. The refractive index n is the dielectric constant ε and n
There is a relation of ² = ε. Therefore, the increment of the refractive index is proportional to the increment of the polarizability α. That is, the refractive index increases in proportion to the substitution amount of the high polarizability ions.

When a high polarizability ion is locally introduced, a high refractive index portion is locally formed. An optical waveguide can be produced by continuously introducing high polarizability ions.

In order to make the refractive index of the optical waveguide have a square distribution, the ions may be distributed such that the ion concentration is high at the center and the ion concentration decreases in proportion to the square of the distance r.

Prior art J. Viljanen et al., "Fabrication of optical strip wa"
veguides with nearly circular cross section by sil
ver ion migration technique, "J.Appl.Phys.Vol.51, N
o.7, p3563 (1980) proposes a method for manufacturing an optical waveguide as shown in FIG. The optical waveguide shown in FIG. 1 is formed by laminating silver ion on the surfaces of two glass substrates to form a plane-symmetric high refractive index region and bonding the regions.

Since two pieces of glass having a high-refractive area having a semicircular cross section are laminated together, a waveguide having a circular high-refractive area can be formed.
The silver ions are forcibly transported into the glass by the action of the electric field. Instead, sodium ions are partially removed from the inside of the glass to the opposite surface.

Fig. 2 shows the configuration of electric field application by J. Viljanen et al. This is done dry without melt. Ag thin film pattern 1
Are linearly deposited on the glass substrate 2. Al thin films 3 and 3 are vapor-deposited on the upper and lower surfaces of the glass substrate 2. This will be the electrode. In this example, a static voltage of 30V is applied between the plates. The temperature is 220 ° C. The manufacturing method is as follows.

(1) A silver thin film pattern 1 having a thickness of 0.2 to 1 μm is formed on a soda glass 2 by photolithography.

(2) Deposit aluminum films 3 and 3 on both surfaces of the glass 2. This becomes an electrode.

(3) Heat to 220 ℃. A voltage of +30 V is applied between Al electrodes with the silver thin film as the positive electrode.

Since both Ag ⁺ ions and Na ⁺ ions are positive ions, they are transported in the direction of the electric field. Ag ⁺ is introduced inside the glass surface. Soda glass contains 12.8 wt% Na ₂ O. This Na ⁺ ion is exchanged with Ag ⁺ ion. Na ⁺ , Ag ⁺
Both proceed in the direction of the cathode. Ag ⁺ enters the glass, and all Na ⁺ goes toward the cathode and partially enters the cathode.

(4) Stop applying voltage. The graph of FIG. 3 shows the silver concentration distribution in the depth direction. C ₁ (x, 0) is the distribution immediately after electric field transport. The distribution is close to the step function.
This is because the transport is by electric field. 5 in the depth direction
Only about μm spread. Now there's a temperature of 22
The temperature is raised from 0 ℃ to 370 ℃, and Ag ⁺ and Na ⁺ ions are diffused by heat. I did this for 2 hours (7200 seconds). Thermal diffusion is not performed by supplying Na ⁺ on the surface of the glass, Na ⁺ is not increased,
Ag ⁺ doesn't decrease either. Ag ⁺ peak is reduced and concentration distribution is 20μ
It spreads to about m. This is the C ₁ (x, 7200) curve.

The value of 1.0 on the vertical axis in Fig. 3 is 12.8 in soda glass.
All of the Na ⁺ ions contained in wt% are replaced with Ag ⁺ ions. The operation of (4) increases the depth of the waveguide by causing silver ions to penetrate further into the interior. At the same time, if the Ag ⁺ ion is 100%, the refractive index becomes too high, which has the implication of correcting this.

A plane-symmetric waveguide is formed on two glass sheets by the methods (1) to (4). Two pieces of this symmetrical glass are stuck together. Thus, the optical waveguide as shown in FIG. 1 is manufactured. If the glass having the same thickness is used, the optical waveguide can be formed just at the central depth of the glass.

However, this method has drawbacks. First of all, we have to make two glasses with Ag ⁺ distribution at the position of perfect plane symmetry. This is a difficult task because the optical waveguide is a thin line. Even if two pieces of glass are bonded together, if a gap is generated, the propagation loss of light becomes large. If the refractive index of the adhesive is different from that of the waveguide, light will be scattered at the boundary. Further, there is a drawback that it is difficult to form an optical waveguide having a refractive index square distribution suitable for the GI type fiber.

T. Izawa et al., "Optical waveguide fromed by eleotr
"ically induced migration of ions in glass plates."
Appl. Phys. Lett., Vol. 21, No. 12, p584 (1972) proposes a method for double electric field transport in a molten salt containing ions. Regarding the refractive index, a step index type waveguide can be formed. A glass substrate is immersed in a molten salt such as AgNO ₃ or TlNO ₃ and an electric field is applied to introduce Ag ⁺ or Tl ⁺ ions into the glass. After that, electric field transport is performed in the molten salt of NaNO ₃ to introduce Na ⁺ ions to the same surface, and the lid is covered with Na ⁺ ions. Thus, the high polarizability ions are confined inside. An optical waveguide can be made inside the glass.

FIG. 4 schematically illustrates the electric field transport configuration of T. Izawa et al.

Molten salt containing Ag ions or Tl ions (Ag
NO ₃ melt, TlNO ₃ melt) 12 is contained. Glass 13 is dipped in this. Below the glass 13 is the Pt electrode 14. There is a dent on the upper surface of the glass, and molten salt also enters here. Another electrode 15 is provided here. The temperature of the molten salt is monitored by the thermocouple 16. In this method, the substrate is heated and Ag ions and the like in the molten salt are introduced into the substrate by the action of an electric field. This includes a process consisting of a first stage (A) and a second stage (B).

(A) Soda glass (or potassium glass may be used) 13 is put in a molten salt 12 containing Ag or Tl ions.
Both molten salt and glass are heated. A voltage is applied between the anode 14 and the cathode 15. Since the temperature is high, the ion mobility in the glass is high. Due to the action of the electric field, silver ions and the like enter the inside of the glass. In this way, FIG.
A refractive index distribution as shown in (a) is obtained. The concentration of ions having a higher polarizability than Na, such as silver ions, is proportional to the increment of refractive index. Therefore, the vertical axis is the refractive index instead of the ion concentration.

(B) In the second stage, the molten salt is replaced with another one. The molten salt contains the ions originally present in the glass.
Since it is soda glass in this example, Na containing Na ions
A molten salt of NO ₃ is used. Solid NaNO ₃ is heated to form a melt. An electrostatic field is applied between the electrodes in the same arrangement. All ions in the glass move in the same direction. Ag ⁺ ions move upward and Na ⁺ ions enter from the bottom surface of the glass.
Then, a refractive index distribution as shown in FIG. 5 (b) occurs in the glass.

In the method of Izawa, electric field transport is performed twice to form a local high refractive index region inside the glass. But both times due to electric field Ag ⁺
Since it is the transport of ions and Na ⁺ ions, the concentration of ions becomes a constant value in a certain region. As shown in FIG. 5 (b), the maximum portion has a flat distribution. This is a step index type refractive index profile. This is sufficient for SI type optical fibers. However, it is poorly connected to the gray index index type optical fiber. This is because the mode conversion loss becomes large.

Shoko 50-38342 (Izawa) denies heat diffusion. This is because silver ions exist in a high concentration only in the vicinity of the surface in thermal diffusion and do not enter the inside of the glass at a high concentration. Therefore, the ion transport by the electric field is performed twice by changing the ions.

Glass is immersed in a molten salt containing ions having a high polarizability such as silver, and electrodes are provided above and below the glass. The molten salt and glass are heated to a temperature higher than the melting point of the salt. High polarizability ions (such as Ag) are forced into the glass by applying a voltage to the electrode field and by the force of the electric field. Then, a step-functional silver ion distribution is formed in the glass. This is similar to that shown in FIG. 5 (a).

Then, the molten salt is replaced with NaNO ₃ containing sodium, and the same electric field transport is performed. Na ⁺ ions enter from this surface, and Ag ⁺ ions are pushed to the other side. Therefore, a refractive index profile as shown in FIG. 5 (b) can be obtained.

In this case, the flat portion of the high refractive index portion is wide and the refractive index square distribution is not obtained. This inventor, Tatsuo Izawa, is from Appl.Phys.
Since it conforms to Lett. Vol. 21, No. 12, p584 (1972), it is considered that both represent the same inventive idea. Izaw
In the method a), electric field transport of different ions is performed twice to create a rectangular high refractive index region distribution. Izawa denies heat diffusion. In thermal diffusion, the distribution of ions is localized near the surface, so that a waveguide can be formed only on the surface. The glass surface has many defects such as irregularities and scratches. When light propagates on the surface, it is scattered by the defects. Not desirable. Therefore, it is necessary to form a high refractive index part inside and form an optical waveguide inside.

Unidirectional electric field transport is suitable as a method for introducing ions deep inside. Since the thermal diffusion has no direction, the ion penetration is slow and inefficient, and the ions do not enter the inner part. So Izawa denies heat diffusion. Two electric field transport is adopted.

However, the electric field transport alone makes the distribution square. It is not possible to create a circular distribution like the square distribution. The present invention, unlike Izawa, wants to make an optical waveguide in which the refractive index is squared. How can the corners of the distribution be rounded? What is the difference between thermal diffusion and electric field transport? This is the problem. Consider the motion of ions in glass. In the case of thermal diffusion, the distribution of Ag ion is Can be argued by the equation of diffusion. x is on the surface and is taken inward with x = 0. D is the diffusion coefficient. Solving this under the condition that t = 0 and c = δ (x) (δ (x) is a delta function), Becomes This is a glass function with standard deviation And the height is Is a function that is.

If, when between molten salt and glass finite time t = 0 to t ₁ is in contact, the concentration distribution Becomes However, erfc is obtained by subtracting the error function from 1, and when x ≧ 0 (erfc = 1 when x <0) Is a function defined by. erfc (x) is 1 at x = 0, but it is a function that decreases sharply after leaving x = 0. From the equation (3), the behavior regarding the time t is well understood. When t is small, the decrease at x ≠ 0 is particularly remarkable. However, as t increases, the value of c (x.t) where x ≠ 0 also increases. Also The value when x is constant is invariable, so the value of x that crosses the straight line c (x, t) = c ₀ with a certain concentration is the square root of time t You can see that it increases in proportion to.

This is because when we consider ions with a certain concentration, It can be considered that it is proportional to. Considered as speed Proportional to. In other words, ions do not diffuse into the inside even if it takes a long time.

FIG. 7 (c) shows the concentration fraction of silver Ag (or K) in the glass by thermal diffusion. The curve as shown in equation (3) is x
When ≠ 0, the value sharply decreases. It turns out that it doesn't spread much even after 6 hours.

On the contrary, consider what happens in the case of electric field transport. First, it is assumed that there is no diffusion term and only electric field transport occurs purely. The concentration distribution equation is Becomes E is the electric field, μ is the mobility, and Eμ is the velocity of the ions in the glass. The initial condition is t = 0 and c (x,
0) = 1 x ≦ 0. That is, the step function θ (x)
(6) is easily solved by giving the initial condition c (x, 0) = θ (−x) (7) at t = 0 by using (1 for x ≧ 0, 0 for x <0). Then, c (x, t) = θ (Eμt−x) (8). That is, if x ≦ Eμt at any time t, c
If (x, t) = 1 and x> Eμt, c (x, t) = 0
Is. At x = Eμt, the value of c (x, t) drops from 1 to 0. Change the step function. This is natural because it carries ions at a uniform velocity in the electric field.

This is the case for pure electric field transport. Actually, diffusion due to heat (thermal diffusion) also occurs at the same time, so the equation is obtained by adding (1) and (6).

If this is solved at t = 0 again under the initial condition of c (x, 0) = θ (−x), It means that. In the limit of tD → 0, (10) coincides with (8) and becomes a staircase function. (1 when Eμt ≧ x, 0 when Eμt <x).

If Dt is finite, the corners of the staircase function will be rounded and rounded.

FIG. 7 (D) is the ion concentration fraction after 20 minutes, 40 minutes, and 1 hour when electric field transport was performed. This is proportional to time c
The area where = 1 is surely increased. In essence, the step function θ (Eμt-x)) Therefore, it is rounded.

From such a consideration, it is found that thermal diffusion is not suitable for transporting ions deep inside the glass. However, this has the effect of rounding the distribution function.
Electric field transport is optimal for transporting ions deep inside the glass. On the other hand, however, the distribution tends to be a step function and tends to be a rectangular distribution. It is difficult to make a squared refractive index distribution. The method of Izawa et al. Is difficult in this respect.

However, the fatal drawback of repeating the electric field transport twice for different ions is another. That is, the refractive index difference corresponding to the refractive index difference between the optical fiber core and the cladding cannot be given to the center and the peripheral portion.

The difference in refractive index between the core and the cladding of the optical fiber is about 1% in the multimode fiber and about 0.3% in the single mode fiber. Not a big difference. In order for the optical waveguide to be well coupled with the optical fiber, it is necessary that mode conversion does not occur so much. Therefore, it suffices that there is a difference in the refractive index difference between the core and the cladding even inside the optical waveguide.

If electric field transport is used twice, as shown in Fig. 5 (b), N
The a ⁺ ion is replaced by 100% Ag ⁺ ion, but there is always a part. For example, the electronic polarizability of Na ⁺ ion is 0.4 ×
10 ^-12 cm ³ , that of Ag ⁺ ions is 2.4 × 10 ^-12 cm ³ . The dielectric constant of glass is not only due to the electronic polarization of Na ⁺ ions, but the polarization of Si, O, etc. also contributes to this. But,
The electron polarizabilities of Na ⁺ and Ag ⁺ differ by about 6 times, and
^{When +} is replaced with Ag ⁺ , the change in the refractive index is not limited to about 1%. Reach 10% to several 10%.

To make the difference in refractive index smaller, it would be necessary to leave part of Na ⁺ instead of replacing all of Na ⁺ with Ag ⁺ . However, this cannot be done with two electric field transports.

An optical waveguide made by two electric field transports has a too large difference in refractive index between the center and the periphery. Even if the size matches the size of the optical fiber, more modes will be propagating modes. This is because the number of propagation modes depends on the refractive index difference. Moreover, the junction between the optical fiber and the optical waveguide is not adiabatic. As a result, many dissipation modes occur at the junction of the inlet and disappear at the junction of the outlet.
The loss due to such mode conversion should be minimized.

DISCLOSURE OF THE INVENTION In order to form an optical waveguide inside glass, (1) high polarizability ions are introduced.

(2) Introduce low polarizability ions.

Two iontophoresis operations are required. (2) introduces the same ions (Na ⁺ etc.) as the glass material to cover the optical waveguide. In the past, the stage (1) was studied vigorously, but the stage (2) was not considered so much.

Thermal diffusion is unsuitable for transporting ions to far distances. However, since the step (2) only covers the optical waveguide, there is no need to carry the ions far. On the contrary, thermal diffusion has the effect of rounding the angular distribution of the concentration distribution. In order to secure a good coupling property with the GI type optical fiber, it is necessary to have a refractive index square distribution.

In addition, the difference in the refractive index between the core part and the cladding part should not be too large. Thermal diffusion has the effect of reducing the peak height of high polarizability ions and reducing the difference in refractive index between the core and cladding portions to an appropriate range.

Therefore, in the present invention, the step (1) is performed by electric field transport, and the step (2) is performed by thermal diffusion. The present invention introduces high polarizability ions (eg Ag, Tl) into glass by electric field transport,
The low polarizability ions are then introduced into the glass by thermal diffusion.

The electric field transport of (1) may be dry type as shown in FIG. 2 or wet type as shown in FIG. In the method of FIG. 2, a silver thin film is vapor-deposited on glass, an Al electrode is attached to the outside, and a voltage is applied between the Al electrodes. Metallic silver causes migration due to the electric field. This has the advantage that the device is simplified because it is dry.

The method shown in FIG. 4 uses molten salt. It is a wet method, and there are some difficulties in manufacturing electrodes and controlling the temperature of salt.
However, since it exists as an ion from the beginning, electric field transport occurs immediately.

In any case, the high polarizability ions can be introduced into the glass by the electric field transport in the first step. This has a distribution close to a step function. Actually, the profile is determined not only by E (electric field) but also by the mobility μ and the diffusion coefficient D.

Using the method shown in Fig. 2, the Ag concentration distribution after applying a voltage and current for 3.05 hours shows the uppermost graph in Fig. 6 τ = 1 × 10 ^-4.
(3.05 hours). Where τ is the normalized time.

Next, the glass is immersed in a molten salt containing low polarizability ions (Na ions in the case of soda glass) originally contained in the glass to heat and diffuse the glass. This causes silver ions to escape from the surface and sodium ions to enter instead. Many silver ions are lost from the surface (movement to the left in Fig. 6). However, a part of it moves to the right and goes inside the glass.

FIG. 6 shows the concentration distribution of silver when electric field transport is performed by τ = 1 × 10 ⁻⁴ and then thermal diffusion is performed.
In the graph, the inside is the real time, and the outside is the normalized time. This is the time including the electric field transport (τ = 1 × 10 ^-4 , 3.05 hours). Therefore, in order to obtain the thermal diffusion time, from the time shown in the graph, 1 × 10 ^-4 , 3.
05 hours need to be deducted.

For example, τ = 1.1 × 10 ^-4 , 3.36 hours (0.31 hours for thermal diffusion)
The peak has fallen to 0.83. Also τ = 1.5 × 10 ^-4 , 4.6
At time (1.45 hours for thermal diffusion) the peak falls to 0.57. Furthermore, at τ = 3, 9.2 hours (thermal diffusion 6.15 hours), the peak falls to 0.3.

In any case, the peak of the concentration distribution is more rounded, and is similar to the square function. This can give the refractive index squared distribution.

The most important thing is that the value of the silver concentration peak can be freely specified according to the time of thermal diffusion. This is something that electric field transport cannot do.

From the core and cladding refractive indices of the optical fibers to be bonded, it is desirable that the silver concentration fraction at the peak point is, for example, 43% (Na fraction is 57%). In this case, it is immediately clear that the normalized time of thermal diffusion should be 1 × 10 ⁻⁴ (actually 3.05 hours). This can be seen from the fifth graph from the top. If the desired peak fraction is 0.3, the thermal diffusion time will be 5.15 hours (6th graph).

In this way, the fraction of the silver concentration peak can be freely determined.
It is a remarkable advantage.

In FIG. 6, the horizontal axis represents the value (0 to 0.1) obtained by dividing the glass thickness L (1 mm) by the depth d. The vertical axis is the silver concentration fraction. 1.0 is the concentration when all Na ⁺ ions are replaced by silver.

Here, the normalized time τ is the product Dt of the diffusion coefficient and time.
Is represented. As described above, time is included in the formula only in the form of Dt, and therefore it is convenient to represent time by Dt. Here, D = 9.1 × 10 ⁻³ μm ² / sec is set to correspond to the real time. 3.05 hours is 10980 seconds, so
At this time, Dt = 1 × 10 ⁻⁴ mm ² . The unit of normalized time is mm ² . Since this is a value obtained by dividing (x-Eμt) ² , x-Eμt can be discussed in this unit when the unit is mm.

To consider the correspondence between the optical fiber core and the cladding,
Of course, it is not enough that the refractive index difference between the center and the peripheral edge is the same. It is required that the spread of the region having the difference in refractive index is almost the same as the diameter of the core. That is, there are at least two parameters.

As described above, the difference in refractive index can be freely set to a smaller value rather than 1.0 as the silver fraction. This can be specified by the thermal diffusion time. Also, although it is the area expansion, this cannot be adjusted by specifying the time of the first electric field transport.

In Fig. 6, a graph immediately after electric field transport (τ = 1 × 10 ^-4 m
m ² ) is rounded up and down, but this Is much larger than Eμt. Eμt If it is made larger than, the angular distribution can be obtained with τ = 1 × 10 ^-4 .

In the present invention, the time t ₁ during the electric field transport in the first step and
Second stage thermal diffusion time t ₂ , electric field strength E, and temperature T
(Influencing D) is a parameter that can be freely selected.
Since there are four parameters, an optical waveguide having a desired refractive index difference and a desired profile can be manufactured.

Example (1) Glass Soda glass or potassium glass is used as a substrate.

(2) There may be various combinations depending on the type of ionic glass to be moved into the glass. Here, Ag ⁺ or K ⁺ is introduced on soda glass.

(3) Measurement of diffusion constant and mobility A thin film of silver is deposited on a glass plate, and aluminum is further deposited on both sides to form electrodes. For example, an electric field is applied at 220 ° C. to cause silver migration. Or AgNO ₃
The glass substrate is dipped in the molten salt of, and a voltage is applied between the electrodes (Fig. 4) to introduce silver ions into the glass. In this case, the melting point of AgNO ₃ is 212 ° C, which is higher than 220 ° C.
℃.

When K ⁺ ions are added, the melting point of KNO ₃ is slightly higher than 334 ° C. 3
Perform at about 40 ° C. These ions are introduced, for example, for 20 minutes to 6 hours without passing an electric current. After that, the ion concentration distribution is actually measured as a function of depth. Then Fig. 7 (c)
Get a graph like. With this The value of D can be obtained by combining

Next, a voltage is applied between the electrodes to introduce ions for about 20 minutes to 1 hour. After that, it is measured as a function of the depth of the ion concentration distribution. A graph as shown in FIG. 7 (D) is obtained.

Then, the mobility μ can be obtained by fitting In this way, D and μ are obtained.

(4) Diffusion constant measurement A glass plate with appropriate Ag and K concentration distribution was treated with NaNO ₃ at 310 ℃.
Immerse in the solution (NaNO ₃ melting point 306.8 ° C.). Again, change the time from 10 minutes to 6 hours. The ion concentration distribution of these Ag and K is measured. There are always two types of diffusion constants. This is due to the difference in temperature.

In this way, two diffusion constants and mobility μ can be obtained. By using these values, E, t ₁ and t ₂ can be changed to form an optical waveguide having an arbitrary ion concentration.

Effect (1) It is possible to obtain an optical waveguide having a desired two-dimensional pattern in bulk glass without using means such as expansive alignment of components and adhesion.

(2) In order to improve the coupling with the optical fiber, it is possible to make the refractive index distribution in the depth direction close to a square distribution, and to match the refractive index difference between the core and the cladding.

[Brief description of drawings]

Figure 1 is a schematic diagram of the optical waveguide proposed by J. Viljanen et al. FIG. 2 is a cross-sectional view showing a structure proposed by J. Viljanen et al. For carrying out electric field transport of silver ions in glass. FIG. 3 is a silver concentration distribution map of the waveguide created by J. Viljanen et al. With the structure of FIG. C ₁ (x, 0) is a graph immediately after electric field transport. C ₁ (x7200) is a silver concentration distribution map after thermal diffusion for 7200 seconds (without changing ion species) after electric field transport. FIG. 4 is a diagram showing the function of immersing glass in a molten salt proposed by Izawa et al. And applying an electric field to transport ions in the glass. Fig. 5 is a refractive index distribution curve in glass obtained by T. Izawa et al. With the structure shown in Fig. 4. Figure 5 (a) shows the distribution curve immediately after the electric field is transported.
Fig. 5 (b) shows the refractive index distribution curve after the molten salt was replaced with the one containing ionic species in the glass and the electric field was transported again. FIG. 6 is a graph showing the ion concentration distribution when high polarizability ions are field-transported into the glass according to the method of the present invention and then thermally diffused in a molten salt of low polarizability ions. The parameters are the normalized time (Dt) and the real time t. FIG. 7 (c) is a concentration distribution graph with time as a parameter when Ag or K ions are introduced into the glass only by thermal diffusion. FIG. 7 (D) is a concentration distribution graph with time as a parameter when Ag or K ions are introduced into the glass by electric field transport. 1 …… Silver thin film 2 …… Glass 3 …… Aluminum thin film 11 …… Molten salt tank 12 …… Molten salt 13 …… Glass 14 …… Polar electrode 15 …… Anode 16 …… Thermocouple

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Shinnosuke Sawa, 1-539, Koya-cho, Matsuyama-shi, Ehime Prefecture, Chiu-Ris Dogo 216, No. 216 (72) Hiroyuki Yoshida, 3-6-5 Mozumohoncho, Sakai-shi, Osaka ( 72) Inventor Kenichi Yoshida 1-3-3 Shimaya, Konohana-ku, Osaka City, Osaka Prefecture Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor Kozo Ono 1-3-1, Shimaya, Konohana-ku, Osaka City, Osaka Prefecture Sumitomo Electric Industrial Co., Ltd. Osaka Works (72) Inventor Yozo Nishiura 1-3-3 Shimaya, Konohana-ku, Osaka City, Osaka Prefecture Sumitomo Electric Industries, Ltd. Osaka Works (56) References Japanese Patent Publication Sho 50-38342 (JP, B1) Japanese Patent Publication Sho 48-5975 (JP, B1) J.I. Appl. Phys. Vol. 51, No. 7 pp. 3563 (1980) Appl. Phys. Lett. Vol. 21, No. 12, pp. 584 (1970)

Claims (4)

[Claims] 1. A method of manufacturing an optical waveguide for forming a high refractive index layer in a substrate made of a glassy material, wherein an electric field is applied in a molten salt containing high polarizability ions, or a metal to be an ion is evaporated. An ion having a high polarizability is introduced into the substrate by electric field transport so that an electric field is applied to the substrate. Therefore, a method of manufacturing an optical waveguide, characterized in that ions of low polarizability are introduced into the substrate to shape the refractive index distribution of the substrate. 2. The method for producing an optical waveguide according to claim 1, wherein soda glass is used as the substrate of the glassy substance. 3. The method according to claim 1, wherein silver nitrate and sodium nitrate are used to prepare a molten salt of ions to be introduced into the substrate by the electric field transport and heat exchange. Manufacturing method of optical waveguide of. 4. The method of manufacturing an optical waveguide according to claim 1, wherein quartz glass is used as the substrate of the glassy substance.