JPH03158802A - Optical waveguide and its manufacturing method - Google Patents

Abstract

PURPOSE:To remove the ununiformity of structure which is generated on the boundary surface of a core layer side part and to reduce a scattering loss by coating both the surfaces of the 1st clad layer and a core layer with an intermediate thin layer having compatibility. CONSTITUTION:The 1st clad layer 7 is formed on a substrate 1 consisting of Si or SiO2 glass, ferroelectric material, and so on. The 1st clad layer 7 consists of a SiO2 layer or a layer containing a refractive index controlling additive. The 1st clad layer 7 and the core layer 5 are coated with the intermediate thin layer 8 and the 2nd clad layer 9 consisting of almost the same material as that of the 1st clad layer 7. The thin layer 8 should be characterized by adhesiveness to the surface of the layers 5, 7 and have compatibility with these layers 5, 7, 9. Thereby, a material similar to that of the layers 7, 5, 9 is used for the layer 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a low-loss optical waveguide that eliminates nonuniformity at the interface between the side surface of a core layer and a cladding layer, and a method for manufacturing the same.

[Conventional technology] In recent years, with the progress of optical fiber communications, optical devices have improved in large-scale productivity, high reliability, no adjustment of coupling, automatic assembly,
With the demand for lower loss, etc., waveguide type optical devices that solve these problems are attracting attention.

Among waveguides, silica-based glass waveguides have particularly low loss, and the connection loss with optical fibers is also very low.
It is seen as a promising waveguide of the future.

Conventionally, the present inventors have devised a method as shown in FIG. 5 as a method for manufacturing a silica-based glass waveguide.

In this method, first, as shown in (a) of the same figure, a 1A glass WA2 made of Si02-TiO1 glass is formed on a substrate 1 made of 5i02 glass. The refractive index difference between the glass film 2 and the substrate 1 is about 0.25%, and the film thickness T is about 8 μm.

Next, the sample obtained in (a) was heat-treated at a high temperature of about 200°C to form the core glass 11!2 into a dense film (b), and 1 g of the core glass! Form a WS1x film 3 on 2 (
C), this is thick film core glass TI! This is because the photoresistor alone is insufficient for etching J,2. The thicker the film thickness of WSix #3 is, the better; however, if it becomes thicker, the substrate 1 will warp due to stress, so the upper limit is about 1 μm.

Next, a photoresist is applied on this WS i xMB, and the photoresist film 4 is patterned by photolithography (d).
WSjxJ by dry enching using A4 as a mask
After patterning IQ3, the core glass film 2 is patterned by dry etching using the photoresist film 4 and WSixM3 as a mask (f).

Then, photoresist Wi, 4 and W Si x film 3
(g), and then apply S to the surfaces of the substrate 1 and core layer 5 after
I Ot T i O□-B20. The process is completed by forming a cladding layer 6 made of glass (h).

The refractive index of this cladding NI6 is made equal to that of the substrate 1, and its film thickness is 20 to 30 μm.1 The structural dimensions of the created waveguide are, for example, W = 10 czm, T
= 8 μm, S = 2 μm, and the refractive index difference between the core layer 5 and the cladding layer 6 is 0.25%.

[The problem that the invention tries to solve! ] However, the method for manufacturing the optical waveguide described above requires thick film core glass! i2 can be patterned into a rectangular shape with good verticality, but photoresist M! 4 and WSix
The surface of the side portion of the core layer 5 is likely to be roughened due to minute irregularities on the edges of the v3 pattern.

The method for depositing the cladding layer 6 is to supply raw material gas for the cladding layer into an oxyhydrogen burner, generate glass particles in an oxyhydrogen flame, and deposit the glass particles on the entire patterned surface. A method of forming a transparent rad glass layer by high-temperature sintering is used.

However, in this method of depositing the cladding layer, since the glass particles are subjected to tflVI under normal pressure, many voids are generated at the interface between the uneven surface of the core layer rf11, and these voids interfere with the high-temperature sintering process. Even after a long period of time, it hardly disappeared and became a center of light scattering, leading to the problem of an optical waveguide with a large scattering loss.

Therefore, the purpose of the present invention is to solve the above problems and to
ff! An object of the present invention is to provide a low-loss optical waveguide that eliminates non-uniformity at the interface between the i-section surface and the cladding layer, and a method for manufacturing the same.

[Means for Solving the Problems] In order to achieve the above object, the optical waveguide of the present invention includes a first cladding layer formed on a substrate, and a second cladding layer formed on the first cladding layer. A core layer having a generally rectangular shape with a small cross section, a compatible intermediate thin layer coated with good adhesion on the surfaces of the first cladding layer and the core layer, and a second thin layer formed on the intermediate thin layer. It consists of a cladding layer.

Further, in the method for manufacturing an optical waveguide of the present invention, after forming a core layer having a generally rectangular shape with a small cross section on a first cladding layer, a Si metal alcoholate solution is applied to the surfaces of the first cladding layer and the core layer. Alternatively, a solution containing a refractive index controlling additive is applied to the solution, dried, solidified and heated to form an intermediate thin layer, and then a second cladding is applied on the intermediate thin layer. It forms a layer.

[When forming the working cocoa layer, surface roughness is likely to occur on the side surface; however, the surface of the first cladding layer and the surface of the core layer are coated with good adhesion by a compatible intermediate thin layer. Therefore, these surface irregularities and voids are filled with the intermediate thin layer and become smooth. Therefore, the nonuniformity of M'fl that occurs particularly at the boundary surface of the side surface of the core layer is eliminated, and losses such as scattering loss are reduced.

In addition, according to the above manufacturing method, when applying the /B solution for forming the intermediate layer on the surface of the core layer, the unevenness on the side surface of the :lAM can be filled with the solution to make it smooth. The non-uniformity of the 111I structure occurring at the boundary surface of the side surface of the core layer is eliminated.

[Example] Hereinafter, one embodiment of the present invention will be described in detail based on the accompanying drawings.

In FIG. 1 showing the first embodiment of the optical waveguide, 1 is Si
Alternatively, the first cladding layer 7 is formed on the substrate 1, which is a substrate made of Sin, glass, ferroelectric material, or the like. This first cladding layer 7 is made of SiO□ or S
Refractive index control additive <FL-P, l'i, A to iO□
1. It consists of a layer containing at least one of F-Zn-Ge, Er, Nd, Yb, 1 mm, etc.).

A substantially rectangular core layer 5 having a smaller cross section than the first cladding layer 7 is formed on the first cladding layer 7 .

Like the first cladding layer 7, this core layer 5 is also made of SiO□
, or made of SiO□ containing an additive for controlling the refractive index.

The surfaces of the first cladding layer 7 and the core layer 5 are covered with an intermediate thin layer 8, and a second cladding layer 9 made of substantially the same material as the first cladding layer 7 is formed on the intermediate thin layer 8. has been done. The intermediate i18 has adhesiveness to the surfaces of the core layer 5 and the first cladding layer 7, and these layers 5, 7.
It is also necessary that the second cladding layer 9 has a Japanese name. Therefore, as the material of the intermediate thin layer 8, the same material as the first cladding layer 7, the core layer 5, and the second cladding M9 is used. However, since the optical waveguide having the above structure is finally sintered, it is necessary to fluidize the intermediate thin layer 8 at that time to fill in the irregularities on the surfaces of the first cladding layer 7 and the core layer 5. It is preferable that the softening temperature of the intermediate thin layer 8 be equal to or lower than the softening temperature of each layer 5.7°9.

The thickness of the intermediate thin layer 8 depends on the value of the refractive index, but is usually selected to be several μm (for example, 2 μm) or less.

According to this configuration, the first cladding layer 7 and the core layer 5
Since the surface of is covered with a compatible intermediate thin layer 8 with good adhesion, the unevenness or voids on the surface of the first cladding layer 7 and the surface of the core layer 5 are filled with the intermediate thin layer 8 and smoothed. As a result, structural non-uniformity occurring particularly at the boundary surface of the side surface of the core layer 5 is eliminated, and losses such as scattering loss are reduced.

Note that the refractive index of the first cladding layer 7 is na+, the refractive index of the core layer is nw, the intermediate thin layer is rl+, and the second cladding layer 9
If the refractive index of is n, 2, then n, ≧n + + n
It is set as w>n @l+n e2. n
,.

” n c2 or net≠nc2 * n w
In the case of ``n+, the intermediate thin layer 8 acts as part of the core layer 5.

The relationship between n and n el+ n e2 is n, ≦n w
1 n cl+nc2 or nw≧nl≧ncl, n,
2, that is, n. l+n. 2
When collectively referred to as nc, n + = n. In the case, the intermediate thin layer 8 acts as part of the cladding layer 7.9 (in this case n, ≠n), nw>n
In the case of +>nc, the intermediate thin layer 8 acts as an intermediate layer between the core layer 5 and the cladding layer 7.9, resulting in an optical waveguide composition in which the refractive index of the core layer 5 is equivalently lowered. n 1
< n a, the intermediate thin layer 8 acts as if the difference in refractive index between the core layer 5 and the cladding layer 7.9 is equivalently increased, and the structural non-uniformity on the surface of the core layer 5 is reduced. This has the effect of alleviating scattering loss caused by - and bending loss when a curved optical waveguide is used.

Next, a method for manufacturing the above optical waveguide will be explained with reference to FIG.

First, after forming the first cladding layer 7 on the substrate 1, a slab-shaped core glass film is formed on the first cladding layer 7, and the core glass film is etched into the first cladding layer 7. An all-shaped core 15 with a smaller cross section than M7 is patterned (a).

Next, the entire patterned surface described in ゛, 1771 in water.
7 layers 8 are formed (b). Of these, the simplest and most efficient method for forming the m1'4 layer 8 is to use Si metal alcoholate 78, or add refractive index control 111 to this solution.
The above substrate 1 is immersed in fuchu mixed with sae containing additives, then pulled out of fuchu and smoked dry, then (f) tt
k pl, iT IE (200 to 500 ''C) This is a method of forming the middle ui1 thin layer 8 by baking at a Noah opening.

Another method is to apply the liquid to the first cladding 7 of the substrate 1.
In this method, the coated layer and substrate 1 are rotated with a spinner, and then baked as described above.

Next, a soot-like second cladding N9 is formed on the intermediate thin layer 8.
After depositing (C), a transparent second cladding M9 is formed by sintering at high temperature, and the optical waveguide is completed (d).
.

According to this method, a medium rrf1 thin layer 8 is formed on the surface of the core layer 5.
When applying the solution to form a
8 liquid can be used to fill and smooth the surface, and in particular, it is possible to eliminate structural non-uniformity occurring at the interface between the four surfaces of the core layer 5. Note that the softening temperature of the intermediate thin layer 8 is
If #l is formed with a material rt lower than that of 7.9, the intermediate thin layer 8 will be in a state close to a fluid state in the sintering process (d>), and the uneven surface can be made smoother.

Note that the process (b) of forming the middle riiJ 71 layer 8
If this is performed in a vacuum, voids at the interface between the first cladding layer 7 and core layer 5 and the intermediate thin layer 8 can be easily eliminated.

In addition to the above methods, methods for forming the intermediate thin layer 8 include:
CVD method, Suba/Kling method, electron beam? The i:e method or the like may also be used.

3(a) and 3(b) show a second embodiment of the optical waveguide. This is a structure in which the thickness of the first cladding Ni7 is varied, and the non-uniformity of the lateral path at the discontinuous point X of the interface between the first cladding H17 and the core layer 5 in FIG. This structure is extremely effective in reducing the scattering loss of the optical waveguide due to non-uniformity that occurs when the optical waveguide is formed into a rectangular shape by an etching process.

As shown in the figure, the first part of the 317 layer 5 is formed.
In order to form the first cladding layer 7 in this way, the thickness of the first cladding layer 7 is ti, and the thickness of the other part is slightly thinner (value of 100OA to 2μm) is t.
First, a slab-shaped glass film for the core layer is formed on the first cladding layer 7, and when this glass film is formed into the substantially rectangular core layer 5 by an etching process, the processing and etching time is It is sufficient to make it longer than in the case of the horizontal path in Figure 1 and also etch a part of the first cladding layer 7. This eliminates the discontinuity at the interface between the core layer 5 and the first cladding layer 7. , are continuous, so that the scattering loss in the core layer 5 can be greatly reduced.

FIG. 3(a) shows a case where there is one core layer 5, and FIG. 3(b) shows a case of a coupled optical waveguide in which two core layers 5 are arranged in parallel.

FIG. 4 shows a third example of an optical waveguide.

In this case, the upper surface of the second cladding layer 9 is formed to have a step along the surface shapes of the first cladding layer 7 and the core layer 5. this! According to S-Ken, since the second cladding layer 9 is formed to have a thin average thickness,
Bending loss in a curved optical waveguide can be reduced.

The present invention is not limited to the scope of the above-mentioned embodiments. For example, when the substrate 1 has a refractive index equal to or lower than the first cladding layer 7, the first cladding layer 7 is Substrate 1 may be used instead.

Thereby, the process of forming the first cladding layer 7 can be omitted, and costs can be reduced. The core layer 5 may have a U-shaped curved portion in the longitudinal direction of the optical waveguide, or may have a bent portion.

At least one layer such as a first cladding layer, a core layer, a second cladding layer, and an intermediate thin layer may be formed on the back surface of the substrate 1, and a metal film may be formed on the optical waveguide. The optical waveguide of the present invention may be used to implement a Y-branch coupler, directional coupler, star coupler, or filter. It is possible to configure optical circuits such as the following.

[Effects of the Invention] To summarize, according to the present invention, the following excellent effects are achieved.

(1) Since the surface of the core layer is covered with good adhesion by the compatible intermediate layer 1-, the unevenness and voids on the surface of the first gland layer and the surface of the core layer are filled with the intermediate layer 4. In particular, the non-uniformity of #I structure occurring at the boundary surface of the side surface of the core layer is eliminated, and losses such as scattering loss are reduced.

(2) Furthermore, according to the manufacturing method of the present invention, when applying a solution for forming an intermediate layer to the surface of the core layer, unevenness on the side surface of the core layer is filled with the /8 liquid to make it smooth. This eliminates the non-uniformity of the structure that occurs at the boundary surface of the side surface of the core layer.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a first embodiment of the optical waveguide according to the present invention, FIG. 2 is a flowchart illustrating a method for manufacturing the same optical waveguide, and FIG. 3 is a diagram showing a second practical example of the optical waveguide. , 4th
The figure is a perspective view showing a third embodiment of the guiding wave, and FIG. 5 is a process diagram illustrating a method of manufacturing an optical waveguide that was previously devised by the present inventors. In the figure, 1 is the substrate, 5 is the core layer, and 7 is the first cladding JI.
J, 8 is a thin layer between ψ, and 9 is a second cladding layer.

Claims (1)

[Claims] 1. A first cladding layer formed on a substrate, a substantially rectangular core layer with a smaller cross section formed on the first cladding layer, and a first cladding layer. An optical waveguide comprising a compatible intermediate thin layer coated with good adhesion on the surfaces of a core layer and a core layer, and a second cladding layer formed on the intermediate thin layer. 2. The optical waveguide according to claim 1, wherein the first cladding layer is thick in a portion where the core layer is formed and thin in other portions. 3. The optical waveguide according to claim 1 or 2, wherein the upper surface of the second cladding layer has a step that follows the surface shapes of the first cladding layer and the core layer. 4. Claim 1, wherein the intermediate thin layer is formed of a material whose temperature is lower than the softening temperature of the core layer and the first and second cladding layers.
, 2 or 3. 5. Claim 1, wherein the first cladding layer is substituted by the substrate when the refractive index of the substrate is less than or equal to the refractive index of the first cladding layer.
, 2, 3 or 4. 6. After forming a substantially rectangular core layer with a small cross section on the first cladding layer, apply a Si metal alcoholate solution to the surfaces of the first cladding layer and the core layer, or add a refractive index control additive to the solution. A method for manufacturing an optical waveguide, which comprises applying a mixed solution containing a substance, drying, solidifying and heating it to form an intermediate thin layer, and then forming a second cladding layer on the intermediate thin layer.